THE 
FLOTATION 


OF  THE 
UNIVERSITY 


THIS  BOOK 

is 
Dedicated 

to 
FRANCIS  EDWARD  ELMORE 

and 

ALEXANDER  STANLEY  ELMORE 
in  Recognition  of 

Their 
Courageous  Persistence  and  Engineering  Skill 

in  the 
Development  of  the  Flotation  Process 


THE 

FLOTATION    PROCESS 


Compiled  and  Edited 

by 
T.  A.  RICKARD 

A.R.S.M.,   M.I.M.M.,   M.A.I.M.E. 


FIRST   EDITION 

SECOND  PRINTING 


Published   by  the 

MINING  and  Scientific  PRESS 

San  Francisco 


COPYRIGHT,  1916, 

BY 
DEWEY  PUBLISHING  Co. 


R5- 


PREFACE 

This  book  has  been  prepared  to  meet  the  need  of  the  hour.  Flota- 
tion is  engaging  the  attention  of  a  rapidly  increasing  number  of 
metallurgists,  mill-men,  and  mine-owners.  Information  on  the  subject 
is  lacking.  The  only  book  heretofore  issued  was  written  four  years 
ago,  and  is  now  out  of  date.  In  1912  the  flotation  process  had  hardly 
won  a  foothold  in  the  United  States  ;  today  fully  50,000  tons  of  ore  is 
being  treated  daily  by  the  frothing  or  bubble-levitation  method.  In 
July  1915  the  Mining  and  Scientific  Press  began  to  publish  a  series  of 
articles  describing  current  progress  in  this  new  branch  of  metallurgy. 
These  were  followed  by  a  number  of  interesting  contributions  on  the 
theory  of  the  subject.  All  of  them  are  reproduced  in  this  volume. 
They  claim  no  finality.  The  physics  of  flotation  is  still  a  riddle  un- 
solved; but  the  beginnings  of  investigation  have  been  made.  In  the 
pages  that  follow  will  be  found  the  rudiments  of  a  connected  theory 
explaining  the  phenomena  underlying  the  life  and  activity  of  the 
metallurgic  bubble. 

In  preparing  this  volume,  I  am  under  pleasant  obligation  to  the 
various  contributors;  it  will  not  be  deemed  invidious  if  I  express 
special  indebtedness  to  Messrs.  0.  C.  Ralston,  C.  T.  Durell,  Dudley  H. 
Norris,,  and  "Will  H.  Coghill.  The  reader  will  be  particularly  grateful 
to  Mr.  Ralston,  of  the  U.  S.  Bureau  of  Mines,  for  his  invaluable  article 
on  the  testing  of  ores  by  flotation  and  for  his  resume  of  preferential 
methods.  Messrs.  Durell,  Norris,  and  Coghill  have  helped  to  clarify 
many  obscure  points.  To  the  anonymous  metallurgist  who  wrote  on 
the  experiments  at  the  Mexican  mill  and  on  the  effects  of  soluble  salts, 
I  tender  special  thanks;  also  to  Messrs.  Butters  and  Clennell  for 
their  detailed  account  of  experimental  work  on  flotation  concentrate. 
To  all  of  these  and  to  the  other  contributors,  I  extend  my  hand. 

T.  A.  RICKARD, 

Editor  of  the  Mining  and  Scientific  Press. 
San  Francisco,  March  1,  1916. 


M596511 


TABLE  OF  CONTENTS 

Page. 

A  Glossary  of  Flotation  7 

The  Flotation  Process  T.  A.  Rickard  9 

Flotation  Tests  at  Mount  Morgan William  Motherwell  53 

Oils  Used  in  the  Flotation  Process  Occasional  Contributor  60 

Flotation  of  Copper  Ores J.  M.  Callow  65 

Preferential  Flotation  0.  C.  Ralston  71 

Flotation  at  the  Inspiration  Mine,  Arizona William  Motherwell  83 

Flotation  in  a  Mexican  Mill Special  Correspondent  91 

Froth  and  Flotation W.  F.  Copeland,  Drury  Butler,  and  Jas.  H.  Wise  102 

Flotation  at  Washoe  Reduction  Works,  Anaconda E.  P.  Mathewson  106 

Flotation  at  the  Central  Mine,  Broken  Hill James  Heblard  110 

What  is  Flotation? — I T.  A.  Rickard  126 

Why  is  Flotation? — I , Charles   T.  Dwell  135 

What  is  Flotation? — II T.  A.  Rickard  144 

Surface  Tension  and  Salts  in  Solution Will  H.  Coghill  154 

Air-Froth  Flotation — I W.  A.   Scott  159 

Why  Do  Minerals  Float? Oliver  C.  Ralston  175 

Why  is  Flotation?— II James  A.  Block  187 

Air-Froth  Flotation — II H.  D.  Williams  and  W.  H.  Kenyan  189 

Cyanide  Treatment  of  Flotation  Concentrate  

Charles  Butters  and  J.  E.  Clennell  203 

Flotation  on  Gold  Ores  A.  E.  Drucker  224 

The  Electrical  Theory  of  Flotation — I Thomas  M.  Bains,  Jr.  225 

Notes  on  Flotation   J.  M.  Callow  231 

Disposal  of  Flotation  Residue W.  Shellshear  248 

The  Electrical  Theory  of  Flotation — II Thomas  M.  Bains,  Jr.  258 

Effects  of  Soluble  Components  of  Ore  on  Flotation.. 

Occasional  Correspondent  263 

Flotation— A  Paradox  Dudley  H.  Norris  267 

Flotation  of  Gold  Ores  Charles  Butters  276 

Testing  Ores  for  the  Flotation  Process — I 

0.  C.  Ralston  and  G-lenn  L.  Allen  277 

Testing  Ores  for  the  Flotation  Process — II 

0.  C.  Ralston  and  Glenn  L.  Allen  293 

Molecular  Forces  in  Flotation Dudley  H.  Norris  308 

Flotation-Tests  in  Separating  Funnel  Special  Correspondent  318 

Flotation  Principles C.  Terry  Durell  319 

The  Electro-Statics  of  Flotation F.  A.  Fahrenwald  335 

On  the  Science  of  a  Froth Will  H.  Coghill  344 

Smelting   Flotation   Concentrate    351 

Flotation  on  Dump  Ore   V.  F.  Stanley  Low  354 

Simple  Problems  in  Flotation T.  A.  Rickard  356 

Index    .  361 


A  GLOSSARY  OF  FLOTATION 

ABSORB.    To  drink  in,  suck  up,  like  a  sponge. 

ADSORB.  To  condense  and  hold  a  gas  on  the  surface  of  a  solid,  particu- 
larly metals.  From  L.  ad,  to,  and  sorbeo,  suck  in. 

AGITATION  is  the  act  or  state  of  being  shaken,  stirred,  or  moved  with 
violence.  From  L.  agitatus,  agito,  the  frequent  of  ago,  to  drive. 

BAFFLE.  That  which  defeats  or  frustrates,  hence  the  projections  or 
wings  that  divert  or  interrupt  the  flow  of  pulp  in  a  vessel. 

BUBBLE.  A  globule  of  air  or  other  gas  rising  in  a  liquid;  also  a  vesicle 
of  water  or  other  liquid  inflated  with  air  or  other  gas. 

BUOY.     To  keep  from  sinking,  to  keep  afloat  in  a  liquid. 

COAL-TAR  is  a  thick,  black,  viscid,  and  opaque  liquid  condensed  when 
gas  is  distilled  from  coal.  Such  products  consist  of  soluble  and  insoluble 
substances. 

COAGULATION.  The  state  of  a  liquid  resulting  from  clotting  or  curdling, 
the  act  of  changing  to  a  curd-like  condition. 

CONCENTRATE.  To  draw  or  gather  together  to  a  common  centre.  To  re- 
duce to  a  purer  state  by  the  removal  of  non-essential  matter.  From  L.  con 
or  cum,  with,  and  centrum,  a  centre. 

CONTAMINATE.    To  make  impure  by  contact  or  admixture. 

ELECTRO-STATICS.  That  branch  of  electrical  science  devoted  to  the  phe- 
nomena of  electricity  at  rest  or  of  frictional  electricity. 

EMULSION.  Milkification.  A  liquid  mixture  in  which  a  fatty  or  resinous 
substance  is  suspended  in  minute  globules.  From  L.  emulgeo,  to  drain  out, 
in  turn  from  e,  out,  and  mulgeo,  milk. 

EUCALYPTUS  OIL.  The  oil  distilled  from  one  of  the  Australian  gum-trees, 
the  eucalyptus  amygdalina. 

FAT  is  a  white  or  yellowish  substance  forming  the  chief  part  of  adipose 
tissue.  It  may  be  solid  or  liquid;  it  is  insoluble  in  water;  when  treated 
with  an  alkali,  the  fatty  acid  unites  with  the  alkaline  base  to  make  soap. 

FILM.    A  coating  or  layer,  a  thin  membrane. 

FLOCCULENT  means  resembling  wool,  therefore  woolly.  Coalescing  and 
adhering  in  flocks.  A  cloud-like  mass  of  precipitate  in  a  solution.  From 
L.  floccus,  a  lock  of  wool. 

FLOTATION  is  the  act  or  state  of  floating,  from  the  French  flottaison, 
water-line,  and  flotter,  to  float,  to  waft. 

FLOTATION-FEED.  The  crushed  ore,  pulp,  or  other  mill-product  that  goes 
for  treatment  to  the  flotation  plant. 

FROTH.  A  collection  of  bubbles  resulting  from  fermentation,  efferves- 
cence, or  agitation. 

GANGUE.  The  non-metalliferous  or  non-valuable  metalliferous  minerals 
in  the  ore;  veinstone. 

GRANULATION  is  the  state  or  process  of  being  formed  into  grains  or  small 
particles.  From  L.  granum,  a  grain. 

GREASE.  Animal  fat  when  soft.  Also  anything  oily  or  unctuous.  From 
the  French  graisse. 

LEVITATION.  The  act  of  rendering  light  or  buoyant.  L.  levitas,  light- 
ness, from  levis,  light. 

METALLIC.     Of  or  belonging  to  metals,  containing  metals,  more  particu- 

7 


larly  the  valuable  metals  that  are  the  object  of  mining.    From  L.  metallum. 
ore. 

MINERAL.  Inorganic  constituent  of  the  earth's  crust.  As  used  in  flota- 
tion the  terms  'mineral'  or  'metallic'  particles  hark  back  to  the  French 
(minerai,  ore)  and  Spanish  (metal,  ore)  meanings.  Both  terms  refer  to 
those  valuable  constituents  in  the  ore  that  it  is  the  object  of  the  process  to 
separate  from  the  non-valuable  constituents,  or  gangue.  Sometimes  'metal- 
lic' has  reference  to  metallic  lustre,  one  of  the  chief  characteristics  of 
metals  and  more  particularly  of  those  metallic  sulphides  that  are  especially 
amenable  to  flotation. 

MODIFY.    To  change  in  character  or  properties. 

MOLECULE.  The  smallest  part  of  a  substance  that  can  exist  separately 
and  still  retain  its  composition  and  characteristic  properties;  the  smallest 
combination  of  atoms  that  will  form  a  given  chemical  compound.  From  F. 
molecule,  diminutive  from  L.  moles,  mass. 

NASCENT.  Coming  into  being,  beginning  to  develop.  From  L.,  nascens, 
being  born. 

OCCLUDE.  To  shut  or  close  pores  or  other  openings.  From  L.,  06,  before, 
claudo,  close. 

OLEIC  ACID  is  fatty  acid  contained  in  olive  oil  combined  with  cresoline. 
Although  called  'acid'  it  is  an  oily  substance  and  functions  as  oil  in  flota- 
tion operations;  it  is  contained  in  most  mixed  oils  and  fats,  from  which  it  is 
obtained  by  saponification  with  an  alkali.  From  L.  oleum,  oil. 

OIL  includes  (1)  fatty  oils  and  acids,  (2)  essential  oils,  mostly  of  vegetal 
origin,  such  as  eucalyptus  and  turpentine,  (3)  mineral  oils,  such  as 
petroleum  products,  including  lubricating  oils. 

OILY  and  GBEASY  are  substantially  equivalent  terms.  All  oils  are  greasy. 
Greasiness  suggests  more  viscidity  than  oiliness. 

OSMOSE.  The  tendency  of  two  liquids  or  gases  to  mix  by  passing  through 
a  membrane  or  porous  wall  separating  them.  From  G.  osmos,  pushing. 

PINE-OIL  is  a  derivative  of  wood-tar,  as  phenol  and  cresol  are  derivatives 
of  coal-tar. 

PULP  is  powdered  ore  mixed  with  water. 

SAPONIFICATION.     Conversion  into  soap;   the  process  in  which  fatty  sub- 
stances form  soap,  by  combination  with  an  alkali.    From  L.  sapo  (w-),  soap. 
SCUM.    Impure  or  extraneous  matter  that  rises  or  collects  at  the  surface 
of  liquids,  as  vegetation  on  stagnant  water,  or  dross  on  a  bath  of  molten 
metal. 

SKIN.    An  outside  layer,  coat,  or  covering.    From  A.  S.  scinn,  ice. 
SPITZKASTEN.     A  pointed  box  or  inverted  pyramidal  vessel,  with  an  out- 
let at  its  point  for  the  separation  of  the  components  of  an  ore  by  gravity. 
German,  spitze,  point,  hasten,  chest. 

SURFACE  TENSION  is  the  contractile  force  at  the  surface  of  a  liquid  where- 
by resistance  is  offered  to  rupture. 

VESICLE.  A  small  bladder-like  cavity  or  hollow  sphere  of  liquid.  From 
vesicula,  diminutive  from  vesica,  bladder. 

VISCOSITY  is  the  property  of  liquids  that  causes  them  to  resist  instan- 
taneous change  of  their  shape  or  of  the  arrangements  of  their  parts :  internal 
friction;  gumminess.  From  L.  viscum,  birdlime. 


THE   FLOTATION   PROCESS 

By  T.  A.  RICKARD 
(From  the  Mining  and  Scientific  Press  of  March  4,  18,  and  April  1,  1916) 

^INTRODUCTORY.  It  is  not  yet  four  years  since  the  starting  of  the 
first  American  mill  using  the  frothing  method  of  flotation,  yet  55,000 
tons  of  ore  is  being  treated  daily  by  this  process  in  the  United  States 
today.  This  means  20,000,000  tons  per  annum.  The  larger  part  of 
these  metallurgical  operations  began  within  the  last  two  years.  It  is 
evident  therefore  that  the  process  is  gaining  ground  so  rapidly  as  to. 
command  the  intelligent  attention  of  all  those  engaged  in  mining. 
In  the  present  writing  upon  the  subject  I  have  tried  to  supply  such 
information  as  is  required  by  those  newly  interested  in  flotation, 
either  as  students  or  as  operators.  Of  course,  what  I  have  written 
makes  no  claim  to  finality,  for  I  am  conscious  of  possessing  only  an 
elementary  understanding  of  the  extremely  abstruse  set  of  phenomena 
underlying  the  process.  My  contribution  is  that  of  a  detached  ob- 
server, eager  to  be  helpful  to  the  workers  in  this  new  branch  of 
metallurgy. 

THE  PHYSICS.  In  a  recent  reminiscence  my  friend  Ben  Stanley 
Revett  has  recorded1  how  he  bet  "a  bottle  of  bubbles"  with  that 
peripatetic  philosopher  Thomas  F.  Criley,  the  partner  of  Carrie  Jane 
Everson  in  an  oil  process  of  concentration  whereby  the  valuable  sul- 
phides were  made  to  float  above  the  worthless  gangue  in  a  pulp  of 
crushed  ore.  Mr.  Revett  says  that  he  bet  his  bubbles  against  Criley 's, 
but  we  suspect  that  in  saying  so  he  was  interpreting  the  prior  art  in 
terms  of  latter-day  metallurgy,  for  it  is  doubtful  whether  any  of  the 
persons  concerned  in  that  early  experiment  at  Baker  City,  Oregon, 
had  a  clear  understanding  of  the  function  of  the  bubbles  in  assisting 
the  oil  to  give  buoyancy  to  the  sulphides,  However,  in  staking  his 
bubbles  of  carbon  dioxide  dissolved  under  pressure  in  the  vintage  of 
Champagne  against  the  performance  predicated  by  Criley,  Mr.  Revett 
must  be  credited  with  successful  anticipation,  for  27  years  after  the 


*This  article  was  presented  as  a  paper  at  the  March    (1916)  meeting  of 
the  Canadian  Mining  Institute. 

i Mining  and  Scientific  Press,  October  16,  1915. 

9 


10  THE  FLOTATION   PROCESS 

incident  we  know  that  the  key  to  the  flotation  process  is  to  be  found 
not  in  the  oil,  the  acid,  or  the  apparatus,  but  in  the  bubbles. 

The  man  who  understands  the  physics  of  a  soap  bubble  has  mas- 
tered the  chief  mystery  of  flotation.  The  small  boy,  who,  as  pictured 
by  Millais,  watches  the  birth,  ascent,  and  bursting  of  the  iridescent 
sphere  of  his  own  making,  is  the  type  of  our  modern  metallurgist  who 
makes  the  multitudinous  bubbles  constituting  a  froth  and  then  won- 
ders to  what  laws  of  physics  this  filmy  product  owes  its  existence. 

To  put  it  briefly,  the  boy,  having  dissolved  soap  in  water,  holds  a 
little  of  it  in  the  bowl  of  his  clay  pipe  while  he  blows  through  tbe 
stem.  The  soapy  water  forms  a  film  that  is  distended  by  the  boy's 
warm  breath  into  a  lovely  sphere,  which  is  lighter  than  the  surround- 
ing air  and  therefore  rises,  while  the  sunshine  undergoes  refraction 
into  the  colors  of  the  spectrum.  When  the  boy  blows  through  his 
pipe  into  pure  water,  he  makes  bubbles  likewise,  but  they  break  in- 
stantly. It  is  the  soap  that  lengthens  their  life.  In  the  language  of 
physics  we  say  that  high  '  surf  ace  tension '  causes  the  pure-water 
bubbles  to  burst  immediately,  while  the  addition  of  soap  introduces  a 
contaminant  that  lowers  the  tension  so  as  to  enable  the  bubbles  to  last 
longer. 

The  basic  factor  in  the  making  of  bubbles  is  surface  tension.  This 
is  the  force  that  causes  the  surface  of  a  liquid  to  resist  rupture.  The 
particles  at  the  surface  have  a  greater  coherence  than  the  similar  par- 
ticles within  the  body  of  the  liquid.  In  other  words,  each  molecule 
within  the  interior  of  the  liquid  may  be  pictured  as  surrounded  by 
molecules  like  itself  in  being  attracted  toward  each  other  equally  in 
all  directions;  while  the  molecules  at  the  free  surface  of  the  liquid 
are  attracted  only  by  those  internal  to  themselves,  the  result  being 
to  constrict  the  free  surface  to  the  least  area.  In  consequence,  the 
surface  acts  as  if  it  were  elastic.  Hence  the  attachment  of  water  to 
the  sides  of  a  tube  and  the  drawing  of  that  water  upward — which  is 
called  'capillarity'  because  it  is  most  marked  in  a  tube  as  small  as 
capillus,  a  hair. 

Numerous  manifestations  of  surface  tension  on  water  could  be 
cited.  Fill  a  tumbler  a  little  more  than  full  and  the  water  will  ha.ve  a 
convex  surface,  indicating  that  there  is  some  force  at  work  to  prevent 
the  water  from  spilling.  Note  the  cohesion  between  two  plates  that 
have  been  wetted.  Dip  a  camers-hair  brush  into  water  and  the  hairs 
cling  together;  immerse  the  wet  brush  in  the  water  and  the  hairs 
separate.  Watch  the  formation  of  a  drop  of  water  and  note  that  it 
behaves  as  if  enveloped  by  a  stretched  membrane.  Water-spiders  can 


THE   FLOTATION   PROCESS  11 

be  seen  running  over  the  surface  of  a  pond  in  summer,  as  small  boys 
run  over  a  pond  covered  with  ice  in  winter.  The  ice  bends  under 
their  weight  without  breaking;  so  also  the  spider2  makes  a  visible 
dimple  without  wetting  his  feet.  The  surface  is  not  ruptured. 

The  force  of  surface  tension  has  been  measured  by  ascertaining 
the  weight  that  can  be  suspended  from  a  film  of  water  in  air.3  It  has 
been  stated  as  3J  grains  per  inch4  or  81  dynes  per  centimetre.5  The 
most  recent  determination  is  that  of  Theodore  W.  Richards  and  Leslie 
B.  Coombs,6  who  found  it  to  be  72.62  dynes  per  centimetre  at  20 °C. 
Many  disturbing  factors  enter  into  the  measurement  of  this  force,  so 
that  divers  figures,  ranging  from  70.6  to  81,  have  been  announced  at 
different  times. 

Surface  tension  differs  as  between  various  liquids  and  fluids  in 
contact;  for  example,  the  tension  separating  mercury  from  water 
amounts  to  418  dynes  per  centimetre,  while  that  separating  olive  oil 
from  air  is  only  36.9  dynes.  A  drop  of  pure  water  will  spread  over 
the  surface  of  pure  mercury  as  oil  will  spread  over  water.  The  sur- 
face tension  of  an  oil-water  surface  is  only  14,  as  compared  with  the 
73  of  an  air-water  surface  at  a  temperature  of  18  °C.7  While  the 
film  of  oil  on  water  may  be  only  one  molecule  thick,  or  one  twenty- 
five  millionth  of  an  inch,  it  will  suffice  to  reduce  the  effective  pull  of 
the  water  surface  from  73  to  43.  This  latter  figure  represents  the 
effective  surface  tension  of  water  modified  by  oil  as  used  in  flotation. 
It  is  the  main  factor  in  the  formation  and  persistence  of  a  bubble. 
Heat  lowers  the  surface  tension  of  water.  Place  powdered  sulphur 
on  the  surface  of  the  water  on  a  horizontal  plate  of  clean  metal ;  apply 
heat  locally ;  the  sulphur  is  pulled  away  by  the  cold  liquid  as  against 
the  feebler  tension  of  the  warmer  liquid. 

This  elastic  force  at  the  surface  of  a  liquid  tends  to  draw  it  into 
the  most  compact  form.  That  is  why  a  drop  assumes  the  form  of  a 
sphere,  in  which  shape  it  presents  the  smallest  surface  in  relation  to 
its  volume.  Surface  tension  is  a  contractile  force.  This  is  shown 
in  a  simple  way  by  blowing  a  soap  bubble  on  the  large,  end  of  a 
pipe  and  then  holding  the  other  end  of  the  pipe  to  a  candle, 
when  the  air  escaping  from  the  shrinking  bag  of  the  bubble 


2ln  New  England  the  boys  call  them  'skaters.' 

s'A  Text-Book  of  the  Principles  of  Physics.'    By  Alfred  Danniell,  1911. 
4C.  V.  Boys  in  'Soap  Bubbles.' 

sClerk  Maxwell  in  the  Encyclopedia  Britannica,  under  'Capillarity.' 
c'The  Surface  Tension  of  Water,  Alcohols,  etc.'    Jour.  Amer.  Chem.  Soc., 
July  1915. 

7'A  Text-Book  of  Physics.'    By  J.  H.  Poynting  and  J.  J.  Thomson,  1913. 


J2  THE  FLOTATION   PROCESS 

extinguishes  the  flame,  as  in  Fig.  1.*  When  water  is  spilled 
on  a  stove,  it  assumes  a  globular  form  and  dances  on  the  hot 
iron  until  it  flashes  into  steam.  When  water  is  sprinkled  on  a  dusty 
floor,  the  dust  forms  a  layer  upon  the  drop  of  water,  which  draws 
itself  together  into  rolling  spherules.  The  smallest  drops  are  the 
most  nearly  round ;  in  the  larger  ones  the  weight  causes  a  flattening, 
because  gravity  overcomes  the  elasticity  of  the  surface  film.  That  is 


FlO.   1.      THE  CONTRACTING  BUBBLE  BLOWS   THE  FLAME. 

shown  even  more  clearly  in  the  case  of  drops  of  mercury,  and  by  the 
beads  of  gold  on  an  assay er's  cupel. 

This  contractile  force  at  the  surface,  whereby  a  portion  of  liquid 
gathers  itself  together  into  spherical  form,  explains  why  the  pure- 
water  bubble  bursts  so  readily.  The  high  tension  shatters  it.  It  does 
not  burst  explosively,  by  expansion  of  the  gas  within  the  envelope, 
but  by  lateral  displacement  of  the  substance  of  the  elastic  film.  It 
collapses  because  the  surface  tension  draws  it  together.  To  prevent 
such  immediate  collapse  it  is  necessary  to  lessen  the  tension,  that  is, 
diminish  the  contractile  force  in  the  elastic  membrane  constituting 
the  film  of  the  bubble.  This  can  be  done  by  introducing  an  impurity 
or  contaminant,  which  lowers  the  surface  tension,  that  is,  diminishes 
the  contractibility  of  the  bubble-film.  Water  has  the  highest  surface 
tension  of  any  common  liquid  except  mercury,  so  that  the  addition 
of  another  liquid  usually  lowers  its  surface  tension. 

Oil  in  emulsion  and  organic  substances  in  solution  can  be  used  for 
this  purpose.  Soap  will  have  the  same  effect,  and  that  is  why  a  soap 

*C.  V.  Boys  in  'Soap  Bubbles,'  page  49. 


THE   FLOTATION   PROCESS  13 

bubble  lasts  longer  than  a  purQ-water  bubble,  the  film  of  the  former 
consisting  of  water  having  some  soap  in  solution.  When  water  has 
been  modified  by  such  a  contaminant,  the  components  of  the  film  can 
so  dispose  themselves  that  the  superficial  forces  will  be  the  same 
everywhere,  that  is,  tend  to  remain  in  equilibrium,  including  the  force 
of  gravity,  which  otherwise  would  pull  the  film  apart. 

When  two  bubbles  come  in  contact  they  tend  to  coalesce  because 
the  two  of  them  have  an  aggregate  area  greater  than  that  required 
to  include  the  same  amount  of  air  within  a  single  bubble.  In  pure 
water  the  bubbles  coalesce  with  a  violence  that  is  mutually  destruc- 
tive. Even  when  a  survivor  is  left,  the  violence  of  coalescence  of  such 
bubbles  in  a  pulp  unhorses  any  mineral  particles  that  may  be  riding 
the  bubbles.  When,  however,  the  water  is  modified  by  oil,  the  con- 
tractile force  of  surface  tension  is  diminished,  the  bubbles  are  less 
fragile,  and  they  survive  long  enough  to  perform  their  metallurgical 
duty  of  buoying  the  metallic  particles  to  the  surface  of  the  liquid 
pulp.  In  practice  the  'modification'  of  the  water  is  effected  by  emulsi- 
fication  or  minute  subdivision  (as  in  a  mayonnaise)  of  an  insoluble 
oil,  such  as  cotton-seed  and  oleic;  or  it  may  be  done  by  means  of  a 
soluble  oil  or  derivative,  such  as  cresol  and  amyl  acetate. 

The  presence  of  a  contaminant  in  water  may  also  affect  its  vis- 
cosity or  internal  friction,  whereby  it  offers  resistance  to  a  change  of 
shape.  This  strengthens  the  film  of  a  bubble  generated  in  such  water. 
Moreover,  it  has  been  asserted8  that  a  concentration  of  the  contami- 
nant occurs  in  the  surface  of  a  liquid,  causing  the  viscosity  to  be  highly 
magnified  as  compared  with  the  body  of  the  liquid.  It  is  also  known 
that  the  films  made  of  any  definite  liquid  are  of  the  same  strength, 
irrespective  of  their  thinness;  so  that  the  attenuation  of  the  skin  of 
a  bubble  does  not  decrease  its  strength.  This  again  follows  from  one 
of  the  most  remarkable  properties  of  a  bubble:  the  ability,  within 
small  limits,  of  adjusting  its  tension  to  the  load.9  Briefly,  the  tension 
at  the  surface  of  a  contaminated  liquid  is  able  to  adjust  itself  within 
fairly  wide  limits.  Thus  a  film  of  such  "a  liquid  can  remain  in  equili- 
brium when  a  film  of  pure  liquid10  would  have  to  break. 


^Samuel  S.  Sadtler  in  Minerals  Separation  v.  Miami  case,  1915. 

^Thermodynamics,'  by  Willard  Gibbs.  Page  313.  "In  a  thick  film,  the 
increase  of  tension  with  the  extension,  which  is  necessary  for  its  stability 
with  respect  to  extension,  is  connected  with  an  excess  of  soap  (or  some  one 
of  its  components)  at  the  surface  as  compared  with  the  interior  of  the  film." 

i«In  a  chemically  pure  liquid  it  is  impossible  to  form  froth  or  multiple 
bubbling.  Some  differentiation  of  the  components  of  a  liquid  is  required  to 
make  a  film. 


14  THE  FLOTATION   PROCESS 

In  his  book  T.  J.  Hoover11  states  how  the  presence  of  a  mere  trace 
of  saponine  will  kill  the  froth  in  the  flotation  cell.  He  does  not  explain 
why.  It  happens  that  saponine,  which  can  be  dissolved  out  of  horse- 
chestnuts,  is  an  aid  to  the  blowing  of  big  bubbles.  But  they  are  weak 
and  tender.  Why?  Because  saponine  increases  the  tension.12  When 
a  saponine  bubble  is  brought  into  contact  with  a  soap  bubble,  the 
former  contracts  and  blows  air  into  the  soap  bubble.  Kayleigh  proved 
that  the  tension  of  the  soap-film  is  only  two-thirds  of  that  blown 
from  a  saponine  solution  of  equal  strength.  One  part  of  saponine  in 
100,000  parts  of  water  will  suffice  to  make  a  liberal  froth.  But  the 
bubbles  are  flimsy.  They  are  so  fragile  as  to  render  them  of  no  use 
as  carriers  of  mineral.  Hence  they  spoil  the  normal  working  of  a 
flotation-cell,  in  which  it  is  necessary  to  employ  a  contaminant  that 
lowers  the  surface  tension  so  as  to  yield  bubbles  that  are  both  per- 
sistent and  sufficiently  robust  to  buoy  mineral  particles. 

In  approaching  the  rationale  of  the  process  under  discussion  it 
may  now  be  assumed  that  we  are  dealing  with  a  pulp  consisting  of  ore 
and  water,  modified  by  oil,  the  ore  having  been  crushed  sufficiently  to 
separate' the  metallic  sulphides  from  the  associated  gangue  in  a  pulp 
consisting  of  minute  particles  of  each.  In  ordinary  water-concentra- 
tion the  lower  specific  gravity  of  the  gangue  permits  the  mill-man 
to  wash  it  away  from  the  heavier  metallic  sulphides,  but  in  the  flota- 
tion process  this  action  is  reversed,  the  metallic  particles  being  lifted 
above,  and  away  from,  the  gangue  particles.  Apparently,  it  is  a 
metallurgic  anomaly.13 

To  this  crushed  ore  we  have  added  oil.  The  oil  serves  as  a  con- 
taminant that  lowers  the  surface  tension;  also  it  augments  the  vis- 
cosity of  the  liquid.  These  two  effects  unite  in  facilitating  the  forma- 
tion of  strong  and  persistent  bubbles.  The  necessary  air  is  introduced 
by  agitation  or  by  direct  injection.  Sea-weed  contaminates  sea-water 
and  makes  foam  in  the  breakers,  as  oil  makes  froth  in  fresh  water 
that  is  agitated. 

Air  has  a  marked  adhesiveness  for  metallic  surfaces:  this  attach- 
ment is  supposed  to  be  enhanced  by  the  presence  of  oil  or  grease  on 
the  metallic  surface.  In  other  words,  the  metallic  surface,  such  as 
that  of  a  sulphide  mineral,  when  in  the  presence  of  both  oil  and  water, 
will  exhibit  a  preference  for  the  oil.  Hence  the  sulphide  is  not  wetted. 

^'Concentrating  Ores  by  Flotation.'     Page  99,  Second  Edition. 
iz'Soap  Bubbles.'    By  C.  V.  Boys.    Page  115. 

"Mr.  Ingalls  has  called  it  'concentration  upside  down;'  Mr.  Norris  has 
called  it  a  'paradox.' 


THE   FLOTATION   PROCESS  15 

This  characteristic  is  less  marked  on  the  part  of  the  heavy  silicates, 
such  as  rhodonite  or  garnet,  and  still  less  evident  in  the  case  of  the 
lighter  silicious  minerals,  such  as  quartz  and  orthoclase.14  The  addi- 
tion of  acid  lessens  the  oil  attachment  to  the  gangue  particles  without 
decreasing  the  selectiveness  of  the  oil  and  the  air  for  the  sulphide 
particles.  Thus  we  can  understand  why  the  bubbles  attach  themselves 
to  the  metallic  particles  and  buoy  them  to  the  top,  while  ignoring  the 
gangue  particles,  which  sink  to  the  bottom  of  the  vessel  in  which  the 
pulp  is  undergoing  stirring  or  agitation.  This  preference  of  air  for 
metals  and  metallic  surfaces  must  be  emphasized.  It  is  the  decisive 
factor  in  the  process  of  flotation.  Most  minerals  when  pulverized,  and 
then  sprinkled  on  water,  will  float,  particularly  if  they  are  in  flakes 
or  plates,  as  gold  often  is  and  as  minerals  with  a  highly  developed 
cleavage  usually  are.  Such  flotation  is  due  to  air,  which  forms  a  dis- 
continuous film  under  the  mineral  particles.  Mickle  proved  this  by 
taking  a  magnetic  mineral,  like  pyrrhotite,  and  pulling  it  out  of  the 
water  by  a  magnet,  when  it  could  be  seen  that  the  water  was  dragged 
up  with  the  mineral.  These  minerals  float  for  the  same  reason  as  an 
ungreased  needle  will  float,  namely,  the  resistance  to  rupture  of  the 
surface  of  the  water  and  the  aid  of  the  air  attached.  It  used  to  be 
supposed  that  the  needle  must  be  greased  in  order  that  it  may  float. 
That  idea,  like  the  general  exaggeration  of  oil  as  a  factor  in  flotation, 
has  been  disproved  by  experiment.* 

If.  to  water  in  which  mineral  dust  is  floating,  an  addition  of  alcohol 
or  caustic  soda  be  made,  or  even  the  vapor  of  alcohol  be  allowed  to  play 
on  the  surface  of  the  water,  the  mineral  particles  will  sink.15  The  con- 
tamination of  the  water  has  decreased  its  surface  tension. 

The  bubbles  collect  the  metallic  particles,  that  is  agreed;  but 
whether  the  selection  is  dependent  upon  the  previous  oiling  is  a  dis- 
puted point.  Apparently  the  adhesiveness  of  air  for  metallic  surfaces 
is  greater  than  that  of  oil,  and  it  would  appear  probable  that  in  the 
flotation  process  the  first  phenomenon  suffices  without  the  aid  of  the 
second.  It  used  to  be  an  accepted  canon  of  flotation  that  the  oil 
coated  the  metallic  particles,  which  therefore  were  not  'wetted'  and 
did  not  sink,  while  the  gangue  particles  were  not  oiled  and  therefore 
were  wetted,  especially  in  acidulated  water,  so  that  they  sank.  Testi- 
mony has  been  given  by  a  keen  observer  that  "the  distribution  of  the 


JiKenneth  A.  Mickle.    Proceedings  of  the  Royal  Society  of  Victoria.    Vol. 
XXIV,  part  2,  1911. 

*See  pages  327  and  356  of  this  book. 


16  THE  FLOTATION   PROCESS 

oil  in  the  concentrate  and  the  gangue  is  entirely  fortuitous. ' >16  It  is 
even  asserted  now  that  instead  of  the  oil  residing  with  the  metallic 
particles  exclusively,  and  leaving  the  gangue  untouched,  it  is  dis- 
tributed throughout  the  mixture.  When  the  larger  proportions  of  oil 
were  employed,  it  is  likely  that  such  promiscuous  oiling  of  all  the 
particles  of  the  pulp  did  take  place,  but  now  that  the  quantity  has 
been  reduced  to  a  proportion  so  small  that  the  presence  of  oil  on  the 
concentrate  is  not  discernible  by  the  senses,  we  may  assume  a  prefer- 
ence for  the  metallic  particles  in  accordance  with  laboratory  observa- 
tion. This  appears  to  be  confirmed  by  experiments  showing  that  in 
the  case  of  specific  minerals,  such  as  chalcocite,  it  is  necessary  to  oil 
the  mineral  in  order  to  lift  it  by  an  air  bubble.17 

When  using  the,  at  present,  minimum  quantity  of  oil — say,  one- 
third  of  a  pound  per  ton  of  ore — it  would  appear  that  the  oil  forms  a 
coating  of  microscopic  thinness  upon  the  metallic  particles.  The 
minimum  thickness  is  the  thickness  of  a  molecule.18 

Metallic  surfaces  have  a  selective  adhesion  for  air  and  for  oil,  as 
we  have  seen.  Therefore  the  molecular  forces  of  the  oil  and  of  the 
metallic  surface  may  be  supposed  to  unite  in  attracting  the  bubbles. 
What  the  nature  of  those  forces  may  be  is  yet  a  matter  of  conjecture, 
although  the  idea  that  they  are  electro-static  is  suggested  by  the  fact, 
among  others,  that  the  metallic  sulphides  most  amenable  to  flotation 
are  good  conductors  of  electricity.19 

The  foregoing  statement  of  physical  principles  applies  more  par- 
ticularly to  the  frothing  method.  The  history  of  the  '  prior  art, '  as  it 
is  called  in  patent  litigation,  shows  that  the  first  stage  of  the  flotation 
process  as  now  in  vogue  was  performed  by  the  use  of  a  large  propor- 
tion of  thick  oil.  This  is  typified  by  the  bulk-oil  method  of  the 
Elmore  brothers.  It  depends  upon  the  lower  specific  gravity  of  oil 
as  compared  with  water,  so  that  when  mixed  in  a  pulp  of  crushed  ore 
the  oil  rises  to  the  top,  dragging  the  metallic  sulphides  with  it.  This 
also  was  explained  formerly  as  due  mainly  to  the  selective  adhesive- 


i«Bertram  Blount,  testifying  for  Minerals  Separation  in  the  Elmore  appeal 
before  the  Privy  Council.  I  might  add  that  'fortuitous'  is  a  word  that 
describes  other  things  in  the  history  of  flotation  besides  the  oiling. 

"Experiments  of  B.  H.  Dosenbach  in  the  Minerals  Separation  v.  Miami 
suit,  at  Wilmington,  1915. 

is'Oil  Films  on  Water  and  on  Mercury/  By  Henri  Devaux.  Mining  and 
Scientific  Press,  July  31,  1915,  page  156. 

i»The  Electrical  Theory  of  Flotation.'  By  Thomas  M.  Bains,  Jr.  Mining 
and  Scientific  Press,  November  27  and  December  11,  1915.  See  also  page  225 
of  this  book. 


THE  FLOTATION   PROCESS  17 

ness  of  oil  for  metallic  surfaces,  which  prevents  them  from  being 
wetted,  while  the  lack  of  a  similar  affinity  on  the  part  of  the  gangue 
particles  enables  them  to  be  so  wetted  as  to  cause  them  to  sink  to  the 
bottom.  All  of  this  is  measurably  true,  but  the  underlying  fact 
seems  to  be  that  an  excess  of  viscous  oil  causes  the  oiled  particles  to 
adhere  or  stick  together  so  that  they  are  rafted  to  the  top.  It  is 
probable  that  when  thus  collected  in  groups  they  are  more  readily 
floated  on  account  of  their  ability  to  hold  more  oil,  as  compared  with 
individual  particles,  because  the  oil  fills  the  spaces  between  the 
members  of  a  group. 

The  lighter  oils  have  a  specific  gravity  ranging  from  0.8  to  0.95, 
as  compared  with  the  1.0  of  water,  so  that  the  margin  for  flotation  is 
small.  For  instance,  in  the  case  of  a  mixture  of  an  oil  having  a  specific 
gravity  of  0.9  and  of  zinc-blende,  having  a  specific  gravity  of  4,  it  is 
necessary  to  use  6.7  parts  by  weight  of  oil  to  one  part  by  weight  of 
blende  in  order  that  the  mixture  may  have  a  specific  gravity  equal  to 
that  of  water.  Thus  an  ore  containing  20%  blende,  or  400  Ib.  per 
ton,  would  require  the  use  of  over  2680  Ib.  of  oil  in  order  to  float  all  the 
blende  in  the  ore. 

In  true  bulk-oil  flotation,  which,  as  a  matter  of  fact,  was  rarely 
performed,  the  phenomenon  of  surface  tension  does  not  play  a  promi- 
nent part.  It  is  mainly  a  question  of  raising  a  mineral  heavier  than 
water  by  aid  of  a  liquid  lighter  than,  and  not  soluble  in,  water.  The 
emulsification  of  the  oil  was  carefully  avoided  by  Elmore.  In  the 
later  phases  of  flotation,  in  which  the  proportion  of  oil  becomes 
steadily  less,  it  is  aimed  to  emulsify  the  oil  and  air.  The  oil  produces 
a  'micro-emulsion  of  air,'  as  Leverrier  expressed  it.  Thus  the  air  is 
thoroughly  distributed  in  the  pulp  and  the  oil  is  brought  into  intimate 
mixture  with  the  water,  which  is  thereby  modified  and  prepared  for 
the  making  of  persistent  bubbles. 

THE  PROCESSES.  The  application  of  the  various  physical  princi- 
ples outlined  in  the  foregoing  paragraphs  has  taken  diverse  forms,  as 
expressed  in  scores  of  inventions,  only  a  few  of  which  have  been  de- 
veloped into  workable  processes.  The  phenomenon  of  surface  tension 
is  used  directly  in  the  so-called  skin-flotation  methods  of  Hezekiah 
Bradford,  Arthur  P.  S.  Macquisten,  and  Henry  E.  "Wood.  In  the 
first  of  these,  invented  in  1886,  the  pulp  flows  down  an  inclined  plane 
onto  the  quiet  surface  of  water  in  a  vessel,  so  that  the  sulphide  par- 
ticles float  forward  under  the  impetus  of  their  descent  while  the 
gangue  particles  sink.  See  Fig.  2.  The  explanation  is  that  sulphides, 
by  exposure  to  the  atmosphere,  attach  films  of  air  to  themselves,  so 


18 


THE   FLOTATION   PROCESS 


that  they  are  not  wetted  and  move  over  the  so-called  water-skin,  while 
the  gangue,  which  has  remained  wet  throughout  the  operation,  sinks 
through  the  surface  to  the  bottom  of  the  vessel. 

Macquisten  applied  the  same  idea  in  a  tube  cast  with  a  helical 
groove  and  revolved  at  a  moderate  speed.    In  1906  this  method  was 


(Mo  Model.) 


2  Sheets— Sheet  I 


H.  BRADFORD. 

METHOD  OF  SAVING  FLOATING  MATERIALS  IN  ORE  SEPARATION. 

No.  345,951.  Patented  July  20,  1886. 


PlG.   2.      THE  BRADFORD  PATENT. 


THE   FLOTATION    PROCESS 


19 


adopted  in  the  Adelaide  mill,  at  Golconda,  Nevada.  The  ore  con- 
tained 2.2%  copper  as  chalcopyrite,  with  pyrrhotite  and  pyrite,  as 
well  as  some  blende  and  galena.  The  gangue  was  quartzose,  contain- 
ing spinel  and  garnet.  The  tubes  were  of  cast-iron,  6  ft.  long,  1  ft. 
inside  diameter,  and  each  weighed  450  Ib.  See  Fig.  3.  Externally 


FIG.   3.      THE  MACQUISTEN  TUBE. 

these  tubes  were  cast  with  two  tires,  which  rested  upon  supporting 
rollers.  The  discharge-end  was  entirely  open.  The  feed-end  was 
closed  except  for  a  hole  in  the  centre  large  enough  to  admit  the  pipe 
through  which  the  pulp  entered.  Internally  the  tube  was  cast  with  a 
helical  groove  of  f-inch  pitch,  which  was  changed  subsequently  to 
IJ-inch  pitch.  The  discharge-end  was  connected  with  a  separating- 
box,  the  joint  between  this  and  the  tube  being  water-tight,  while  the 
tube  was  free  to  revolve.  At  the  side  of  the  separating-box,  directly 
opposite  the  discharge  from  the  tube,  an  opening  or  lip  was  cut  for 
the  overflow  of  the  surface  layer  of  water,  carrying  the  floating 
mineral.  This  opening  regulated  the  depth  of  water  in  the  tube.  The 
bottom  of  the  opening  was  three  inches  above  the  inside  bottom  of  the 


20  THE  FLOTATION   PROCESS 

tube,  so  that  there  was  three  inches  of  water  in  the  tube  ;  the  feed  and 
the  discharge  were  so  regulated  that  the  water  passing  over  the  lip 
was  about  £z  inch  deep.  The  tube  was  rotated  at  30  r.p.m.  in 
a  direction  corresponding  with  the  helix  of  the  interior.  As  Mr. 
Ingalls  said:33  "The  pulp  is  thus  screwed  through  the  tube  and 
in  its  advance  is  repeatedly  given  an  opportunity  to  slide  upon  the 
surface  of  the  water,  where  it  may  be  retained  by  surface  tension." 
The  ore  was  crushed  to  pass  30  mesh.  The  capacity  of  each  tube  was 
5  tons  per  24  hours,  and  25  tubes  were  in  use.  A  concentration  of 
11:1  was  effected  on  a  2.2%  copper  ore,  the  tailing  assaying  0.2%; 
but  this  refers  only  to  the  deslimed  ore,  that  is  70%  of  the  supply,  so 
that  the  actual  extraction  was  only  63%.  The  inability  to  treat  slime 
is  a  notable  defect  of  this  ingenious  method  of  flotation. 

Wood's  method  is  equally  interesting.  The  ore  is  crushed  dry 
to  30  or  40  mesh  and  is  then  fed  in  a  thin  stream  from  a  vibrating 
plate  onto  the  surface  of  water  in  a  tank  to  the  surface  of  which  a 
forward  movement  is  given  by  small  jets,  also  of  water.  By  a  com- 
bination of  the  capillary  attraction  and  the  pressure  of  a  constant 
feed,  the  sulphides  are  caused  to  move  forward  as  a  definite  elastic 
film  on  top  of  the  water.  This  film  of  mineral  passes  over  an  endless 
canvas  belt,  which  emerges  from  the  tank  at  a  particular  angle,  varied 
according  to  the  kind  of  mineral  to  be  saved.  The  belt  with  its  film 
of  sulphides  passes  over  three  rollers  so  that  its  motion  is  reversed 
when  it  strikes  the  water-level  of  a  second  tank,  where  it  releases  its 
valuable  burden.34  Very  little  gangue  in  suspension  comes  over,  as 
the  water  drains  back  into  the  main  tank.  Any  submerged  particles 
that  have  been  accidentally  wetted  or  are  so  heavy  that  they  have 
penetrated  the  surface-film,  pass  to  standard  concentration-tables,  on 
which  they  are  separated  by  gravity  in  the  ordinary  way.  In  the 
case  of  molybdenite  and  graphite,  the  film  concentrate  is  still  further 
cleaned  by  being  passed  over  a  nearly  vertical  screen.  Gangue  in  sus- 
pension passes  through,  while  the  flat  crystals  of  the  valuable  minerals 
slide  over  the  screen,  which  largely  dewaters  them.  The  flotation  con- 
centrate is  collected  and  dried  as  usual.  See  Fig.  4. 

Mr.  Wood  is  using  his  own  process  to  commercial  advantage  in 
the  treatment  of  molybdenite  ore,  at  Denver.  The  Macquisten  tube  is 


whole  of  the  above  description  is  taken  from  the  admirable  technical 
article  by  W.  R.  Ingalls  in  'Concentration  Upside  Down.'    Eng.  &  Min  Jour 
October  26,  1907. 

3*From  particulars  given  to  me  by  Mr.  Wood  himself.     See  also  Trans. 
A.  I.  M.  E.,  Vol.  XLIV   (1912),  pp.  684-701. 


THE   FLOTATION    PROCESS  21 

still  in  use  at  Mullan,  Idaho;  but  the  Bradford  patent  is  only  of 
academic  interest.  These  methods  have  been  confused  with  the  more 
recent  notation  processes ;  they  ought  to  be  differentiated.  I  suggest 
therefore  that  they  be  classed  under  'film-suspension,'  for  it  may  be 


FlG.    4.       THE    WOOD    MACHINE. 

taken  that  in  every  case  the  sulphides  are  carried  with  air  over  the 
tensional  film  on  the  surface  of  the  water. 

Incidentally,  it  may  be  well  to  point  out  that  although  it  is  con- 
venient to  speak  of  the  'water-skin'  and  of  'skin-flotation,'  the  use  of 
either  'skin'  or  'film'  is  inaccurate.  A  skin  is  a  thing  of  definite 
thickness,  which  therefore  can  be  'peeled'  off,  like  the  epidermis,  for 


22 


THE   FLOTATION    PROCESS 


example.  The  phenomenon  of  surface  tension  involves  nothing  of 
the  kind.  It  refers  to  a  condition  of  molecular  forces  at  the  surface 
of  a  liquid,  the  effect  of  which  can  be  only  one  molecule  thick.  Thus, 


No.  776,145.  PATENTED  NOV.  29,  1904. 

C.  V.  POTTER. 
PROCESS  OF  SEPARATING  METALS  FROM  SULFID  ORES. 

AFPLICATIOH  FILED  JAM.  14,  1902. 
10  MODEL. 


ft. 


FlO.    5.      THE   POTTER   PATENT. 


THE   FLOTATION   PROCESS  23 

'water-skin'  and  'skin-flotation'  stand  for  water-surface  and  surface- 
suspension. 

Neither  Bradford  nor  Wood  uses  oil  or  acid,  but  in  the  later  ap- 
plications of  the  Macquisten  tube  both  have  been  introduced.  As  the 
ore  contains  carbonates  that  would  react  with  the  sulphuric  acid  so 
as  to  liberate  carbon-dioxide  gas,  it  is  obvious  that  another  factor  is 
introduced,  namely,  the  bubble  idea,  which  has  proved  so  potent  in 
the  more  recent  phase  of  flotation.  The  further  addition  of  oil  marks 
a  distinct  departure  from  the  first  idea  of  the  inventor,  causing  the 
process  to  resemble  those  of  Potter,  Delprat,  and  De  Bavay. 

The  methods  of  these  three  Australians  were  alike  designed  to 
treat  Broken  Hill  tailings,  containing  zinc-lead  sulphides  in  a  gangue 
composed  partly  of  carbonates,  notably  calcite,  siderite,  and  rhodo- 
chrosite.  Charles  V.  Potter  used  water  containing  from  1  to  10% 
sulphuric  acid,  which  was  added  to  crushed  ore  placed  in  a  vessel 
(see  Fig.  5)  provided  with  stirrers  (B'  the  shaft  and  B  the  arms.) 
Heat  was  then  applied  by  gas  (3)  ;  whereupon  the  metallic  particles 
rose  to  the  surface  of  the  liquid.  It  has  been  said  that  "it  is  clear 
that  he  (Potter)  had  in  view  a  surface  tension  process."35  if  this  is 
meant  as  a  reference  to  the  surface-suspension  method,  say,  of  Brad- 
ford, it  is  incorrect.  Surely  Potter  used  bubble-levitation  as  his  prin- 
cipal effect.  The  gas  generated  by  the  action  of  the  acidulated  water  on 
the  carbonates  joined  with  the  air  entrained  by  the  ore  is  furnishing 
gas  for  making  bubbles,  this  result  being  assisted  further  by  the 
stirring  of  the  pulp  and  the  heating  of  it.  See  also  Fig.  10. 

G.  D.  Delprat  had  an  apparatus  suggesting  the  employment  of  sur- 
face suspension,  but  he  also  used  chemicals  to  induce  flotation.  See 
Fig.  6.  By  the  addition  (through  the  pipe  5)  of  a  hot  solution  of 
acid  salt-cake  to  the  crushed  ore  as  it  was  fed  (from  the  chute  1) 
upon  a  pan  having  a  sloping  bottom  (4)  heated  by  a  Bunsen  burner 
(14),  the  sulphides  were  made  to  rise  to  the  surface  of  the  vessel 
(at  3,  passing  forward  along  13),  while  the  gangue  collected  in  a 
sump  (10).  In  this  case  also  the  flotation  was  the  result  of  forming 
bubbles  of  carbon-dioxide  gas  and  of  air  by  chemical  action  and  heat. 
Auguste  J.  F.  de  Bavay  described  a  process  in  which  a  thin  stream 
of  freely  flowing  pulp  was  delivered  upon  the  surface  of  a  vessel  of 
water,  after  the  style  of  Bradford.  The  description  of  the  method  as 
used  subsequently  on  the  North  Broken  Hill  mine  does  not  correspond 
with  this,  for  in  that  plant  the  mill-tailing,  relieved  of  slime,  is  said30 


35'Concentrating  Ores  by  Flotation.'    Page  9. 
Page  115. 


24 


THE   FLOTATION   PROCESS 


to  have  been  fed  into  a  vessel  provided  with  a  mixing  device,  run  at 
a  high  speed,  so  as  to  agitate  the  acidulated  pulp.  The  sulphides  rose 
to  the  surface,  much  in  the  same  way  as  in  the  preceding  methods  of 
Potter  and  Delprat.  That  of  Potter  was  used,  in  a  modified  form,  at 
the  Block  14  mine  at  Broken  Hill  in  1905  and  1906,  while  the  Delprat 


No.  763,662.  PATENTED  JUNE  28,  1904. 

0.  D.  DELPRAT. 

APPARATUS  FOR  USE  IN  CERTAIN  PROCESSES  OF  EXTRACTING  SULFIDS 
FROM  ORES. 

APPLIOATIOH  FILED  MAS.  9,  1903. 
10  MODEL. 


FIG.    6.      THE    DELPRAT   PATENT. 


THE  FLOTATION   PROCESS  25 

process  has  been  in  use  for  several  years  successfully  at  the  Broken 
Hill  Proprietary  mine.  It  is  proper  to  add,  however,  that  all  of  these 
acid-flotation  methods  are  now  only  of  academic  interest.  In  the  chief 
application  of  these  processes  it  has  not  been  customary  to  use  oil, 
but  as  the  material  treated  came  from  old  dumps  of  tailing  it  may  be 
assumed  that  there  was  some  substance  present  capable  of  modifying 
the  water  sufficiently.37 

The  first  application  of  any  of  the  oil-flotation  processes  on  a 
working  scale  in  a  mill  was  that  made  at  the  Glasdir  mine,  near 
Dolgelly,  in  Wales,  by  Francis  E.  Elmore  in  1899.  The  mixture  of 
crushed  ore  and  water  was  fed38  at  the  upper  end  of  a  slowly  revolv-. 
ing  drum,  provided  with  annular  helical  ribs  and  transverse  blades,  so 
as  to  effect  the  mixing  of  the  pulp  and  the  oil  without  producing 
emulsification.  See  Fig.  7.  The  oil  was  introduced  through  a  sep- 
arate pipe.  The  mixture  was  discharged  into  a  V-shaped  vessel,  where 
the  water  and  sand  subsided  while  the  oil  buoyed  the  sulphides  to 
the  top.  An  oil-residuum  having  a  specific  gravity  of  0.89  was  used 
in  equal  parts  by  weight  with  the  ore,  ton  for  ton.  The  oil  was  so 
viscous  as  to  require  the  aid  of  small  rotary  pumps  to  propel  it  for- 
ward. The  temperature  of  the  oil  and  water  was  kept  between  54° 
and  57 °F.  The  loss  of  oil  was  2  gallons  per  ton  of  ore.  A  concen- 
tration of  14: 1  was  achieved  with  a  recovery  (in  the  concentrate)  of 
69%  of  the  gold,  65%  of  the  silver,  and  70%  of  the  copper  from  a 
pyritic  and  chalcopyritic  ore  assaying  1.12%  copper,  0.049  oz.  gold, 
and  0.8  oz.  silver  per  long  ton.  The  process  was  described  as  "a 
somewhat  dirty  and  nasty  process/7  It  did  not  work  on  oxidized  or 
earthy  ores,  nor  upon  tarnished  sulphides. 

In  the  course  of  the  discussion  following  the  reading  of  the  paper 
by  Mr.  Rolker  from  which  these  facts  are  gleaned,  it  was  acknowl- 
edged that  the  process  developed  by  Mr.  Elmore  was  based  on  pre- 
vious experimental  work  done,  at  the  same  mine,  by  George  Robson, 
who  used  petroleum  in  even  larger  proportion,  as  much — I  have  been 
informed — as  three  tons  of  oil  to  one  of  ore.  But  the  most  interesting 
fact  elicited  by  the  discussion  was  the  statement  made  by  Mr.  Elmore, 
and  confirmed  by  the  superintendent  of  the  mill,  John  Bevan,  that  the 


37This  suggestion  is  made  by  Mr.  Hoover  in  his  book.  On  page  101  hf» 
says  that  "there  may  be  organic  substances  in  the  ore  which,  upon  the 
addition  of  acid,  yield  gummy  compounds  that  selectively  adhere  to  the 
ore."  By  'ore'  here  he  probably  means  'sulphides,'  that  is,  the  blende  and 
galena. 

sscharles  M.  Rolker.  'Notes  on  the  Elmore  Concentration  Process.' 
Trans.  Inst.  M.  &  M.,  Vol.  VIII  (1899-1900)  pp.  379-384. 


THE   FLOTATION   PROCESS 


actual  load  of  mineral  carried  by  the  oil  was  25%,  as  against  the 
theoretical  load  of  10%  inferred  by  Mr.  Rolker.  In  short,  the  oil  did 
150%  more  than  anybody  could  explain.  The  'prior  art'  was  in  the 
dark,  but  the  posthumous  art  of  today  can  make  a  confident  guess. 


No.  676,679 


Patented  June  18,  1901. 


F.  E.  ELMORE. 
PROCESS  OF  SEPARATING  METALLIC  FROM  ROCKY  CONSTITUENTS  OF  ORES. 

(Application  filed  Apr    10*1899.) 


No  Model.; 


2  Shuts-Sheet  I. 


FlG.   7.      THE  ELMORE  PATENT. 


THE   FLOTATION    PROCESS  27 

Of  course,  the  larger  part  of  the  levitation  was  done  by  air,  entangled 
previously  in  the  ore  particles  and  entrained  subsequently  during 
the  mixing  of  the  pulp  with  the  oil  in  the  drum.  Later  investigators 
can  testify  how  difficult  it  is  to  prevent  the  indrawing  of  air  under 
such  circumstances.  Therefore  even  in  this  beginning  of  flotation  as 
a  practical  process  the  agency  of  air  was  utilized,  although  unwit- 
tingly. Four  years  later  Walter  McDermott,  who  has  been  a  con- 
sistent supporter  of  the  Elmore  brothers  in  their  flotation  business, 
acknowledged  that  "the  agitation  with  the  pulp  results  in  the  oil 
taking  up  a  very  appreciable  quantity  of  air. ' >39 

This  fact  was  not  recognized  at  first,  but  in  1904,  six  years  after 
the  first  bulk-oil  patent  of  1898,  Francis  E.  Elmore  took  out  his  pat- 
ent for  vacuum-oil  flotation.  See  Fig.  8.  In  this  he  subjected  the 
oiled  and  acidulated  pulp  to  a  vacuum,  thereby  releasing  the  air 
dissolved  in  the  water.  The  air  thus  held  in  solution  amounts  to  2.2% 
by  volume,  at  sea-level  and  60  °F.  By  lowering  the  pressure  and  raising 
the  temperature  this  air  is  released,  thereupon  attaching  itself,  in  the 
form  of  bubbles,  to  the  oiled  sulphide  particles,  which  rise  to  the  sur- 
face. For  example,  the  air  in  a  pulp  of  1  ton  of  ore  to  6  of  water 
suffices  to  lift  360  Ib.  of  zinc-lead  sulphides  in  a  Broken  Hill  ore.40 
In  actual  practice,  however,  the  weight  of  sulphides  floated  is  con- 
siderably greater  than  the  theoretical  capacity,  as  based  on  the 
efficacy  of  the  air  released  from  solution  in  the  water.  Part  of  the 
work  is  done  by  the  gaseous  carbon  dioxide  liberated  by  the  reaction 
between  the  acid  and  the  carbonates,  such  as  calcite,  either  in  the 
gangue  or  added  in  the  form  of  limestone.  Part  of  it  is  entangled  in 
the  ore  particles  and  part  of  it  is  entrained  into  the  pulp  during 
mixing.  In  this  process  the  quantity  of  oil  added  to  the  pulp  was 
reduced  to  10  Ib.  per  ton  and  finally,  in  some  cases,  to  as  little  as  3  Ib. 
per  ton  of  ore.  The  machine  devised  by  Elmore  was  remarkably 
ingenious  and  to  it  the  success  of  the  process  was  largely  due.  It  was 
applied  at  many  mines,  notably  the  Sulitelma  copper  mine,  in 
Norway.41 

The  Potter-Delprat  and  the  Elmore  vacuum  processes  are  clearly 
based  on  the  activity  of  bubbles  of  carbon  dioxide  or  air,  or  both. 
Next,  mention  must  be  made  of  Alcide  Froment,  who,  although  he 


39'The  Concentration  of  Ores  by  Oil.'  E.  &  M.  J.,  February  14,  1903,  page 
262. 

*OT.  J.  Hoover.     'Concentrating  Ores  by  Flotation.'     Page  102. 

4i'Vacuum-Concentration  at  Sulitelma.'  Holm  Holmsen  and  H.  N.  Rees. 
The  Mining  Magazine,  May  1910. 


28 


THE   FLOTATION   PROCESS 


LLMORE  VACUUM 
CONCENTRATORS 

Q  IN  EKH  ROW 


FIG.   8.      THE  SULITELMA  PLANT. 


THE  FLOTATION   PROCESS  29 

was  not  the  inventor  of  a  working  process,  introduced  the  idea  of 
violent  agitation  for  the  purpose  of  producing  bubbles  of  gas  rapidly 
from  a  pulp  containing  both  calcite  and  acid.  While  he  looked  to 
carbon  dioxide  as  the  gas  from  which  to  make  his  bubbles,  he  did  un- 
doubtedly entrain  lots  of  air  and  obtained  the  use  of  it  in  generating 
the  bubbles  that  attached  themselves  to  the  oiled  particles.  He  did  not 
recommend  much  oil :  only  l  i  a  thin  layer. ' '  In  his  later  instructions  to 
the  Minerals  Separation  company,  which  bought  his  British  patent  in 
1903,  he  specified  that  the  oil  was  to  be  from  1  to  3J%  on  the  ore. 

The  next  method  was  that  invented  by  Arthur  E.  Cattermole,  also 
in  1902.  It  was  to  buy  his  patents  that  the  Minerals  Separation  com- 
pany was  organized  in  1903  by  John  Ballot,  J.  H.  Curie,  "W.  W. 
Webster,  S.  Gregory,  H.  L.  Sulman,  and  H.  F.  K.  Picard.  Catter- 
mole departed  from  the  prior  art.  Instead  of  floating  the  sulphides, 
he  sank  them,  while  the  gangue  was  assisted  to  rise  in  an  upward 
current  of  water.  He  added  oil  in  the  proportion  of  4  to  6%  "of 
the  weight  of  metalliferous  mineral  present  in  the  ore,"  together 
with  2%  of  soap,  so  as  to  obtain  an  agglomeration  of  flocculent  sul- 
phide particles,  which,  being  heavily  oiled,  stuck  to  each  other,  in 
groups  or  granules  that  sank  to  the  bottom.  He  used  a  Gabbett,*  or 
cone-mixer,  to  obtain  a  violent  agitation  of  the  pulp,  and  followed  it 
by  a  gentler  stirring  during  which  the  separation  into  "shotty  gran- 
ules" was  effected  in  the  presence  of  as  little  air  as  possible. 

This  process  was  only  put  to  work  in  one  mill,  on  the  Central  mine 
at  Broken  Hill,  where  it  must  have  seemed  a  metallurgical  abortion 
during  the  very  short  time  it  was  in  use.  The  oil  was  emulsified  with 
soft  soap  and  then  fed  into  the  mixers,  where  the  crushed  ore  under- 
went agitation  with  acidulated  water.  From  the  very  start  a  con- 
siderable proportion  of  mineral  was  floated  on  the  froth  incidental  to 
violent  mixing  in  the  presence  of  air.  Apparently  only  a  part  of  the 
sulphides  was  *  granulated, '  so  as  to  sink  according  to  program.  The 
remainder  was  floated  unintentionally.  The  description  given  by 
the  manager,  James  Hebbard,  indicates  that  he  and  his  staff  stumbled 
upon  the  so-called  agitation-froth  process  almost  immediately.  He 
records42  how  he  discovered  that  more  froth  was  made  by  using  less 
oil,  and  that  the  frothing  and  floating  proved  a  better  method  than 
the  granulating  and  sinking  of  the  sulphide  particles.  He  also  states 
that  the  discovery  was  made  concurrently  by  the  metallurgist43  of 


42'Flotation   at    the    Central    Mine,    Broken    Hill.'     By   James    Hebbard. 
Mining  and  Scientific  Press,  September  4,  1915. 

actual  operator  was  Arthur  H.  Higgins.  *See  Fig.  41. 


30  THE  FLOTATION   PROCESS 

the  Minerals  Separation  company  in  the  London  laboratory.  They 
hit  upon  the  same  idea  by  varying  the  quantity  of  oil,  in  March  1905, 
so  we  are  told.  Yet  the  plant  at  the  Central  mine  was  allowed  to  start 
on  the  Cattermole  process  in  July.  Successful  tests  with  the  froth- 
ing process  were  not  made  until  September,  the  proportion  of  oil 
being  reduced  from  3%  when  granulating  to  between  0.15  and  0.2% 
when  frothing.  The  plant  was  gradually  changed  until  granulation 
was  completely  ousted,  by  decreasing  the  quantity  of  oil  and  increasing 
the  violence  of  agitation.  The  ore  from  the  mixers  was  passed  with 
"a  good  splash"  into  spitzkasten,  thereby  accentuating  the  need  for 
aeration. 

So  the  failure  of  the  Cattermole  method  is  stated  to  have  led  to 
the  Minerals  Separation  process  of  today,  the  proprietary  rights  to 
which  are  based  primarily  on  U.  S.  patent  No.  835,120,  dated  May  29, 
1905.     This  is  a  process  "wherein,  by  the  use  of  a  frothing  agent, 
and  in  the  presence  of  such  agitation  as  will  maintain  or  produce  dis- 
tribution of  the  ore  particles  through  the  pulp,  and  dissemination  of 
bubbles  of  air  through  the  pulp  and  into  contact  with  the  metallic 
particles  through  the  pulp,  the  air  bubbles  will  seize  the  metallic 
particles  and  will  carry  them  to  and  through  the  surface  of  the  pulp, 
so  as  to  permit  of  their  delivery  at  or  above  the  surface  of  the  pulp 
separate  from  the  gangue  particles. ' '    This  description  is  taken  from 
the  complainant's  brief  in  the  suit  of  Minerals  Separation,  Limited, 
v.  Miami  Copper  Company,  1915.    It  is  further  explained  that  in  this 
process  ' '  the  frothing  agent  is  an  oil  or  immiscible  liquid,  and  the  dis- 
covery was  that  this  mode  of  operation  in  the  concentration  of  ores 
was  attainable  with  small  quantities  of  oil,  quantities  so  small  that 
although  the  oil  coated  the  metallic  particles  in  the  exercise  of  the  well 
known  preferential  affinity  of  oils  for  metallic  substances,  the  coating 
was  so  minute,  so  nearly  infinitesimal,  that  the  oil  disappeared  from 
sight  and  sense.     In  this. process  the  oil  coats  the  metallic  particles, 
modifies  the  water  so  as  to  produce  minute  and  persistent  air-bubbles, 
and  increases  the  attraction  of  the  metallic  particles  for  the  air- 
bubbles;  and  the  persistency  of  the  air-bubbles  is  such  that  the  air- 
bubbles  cling  to  the  metallic  particles  and  carry  them  to  and  through 
the  surface  of  the  pulp,  and  when  the  air-bubbles  escape  from  their 
water  environment  in  the  body  of  the  pulp  and  are  exposed  at  or  above 
the  surface  of  the  pulp,  their  water-films  carrying  a  mineral  load  are 
maintained  intact  until  at  least  their  separation  from  the  body  of  the 
pulp  has  been  effected,  by  overflowing  or  otherwise.    The  air-bubbles 
with  their  mineral  load  form  a  froth  floating  upon  the  surface  of  the 


THE   FLOTATION   PROCESS  31 

pulp,  which,  if  allowed  to  remain  there  in  a  quiescent  condition  will 
float  for  days  and  weeks.  This  froth  has  therefore  been  properly 
called  a  persistent  or  permanent  froth.  It  will  always  form  a  coherent 
mass  of  bubbles  pressed  against  each  other  and  frequently  several 
inches  in  thickness. " 

This  description,  lacking  adequate  punctuation,  as  is  usual  in  legal 
statements,  may  be  accepted  as  official,  being  the  product  of  a  joint 
effort  on  the  part  of  counsel  and  experts  representing  Minerals  Separa- 
tion in  the  lawsuit  at  Wilmington.  In  the  basic  patent,  No.  835,120, 
the  proportion  of  oil  is  given  as  "a  fraction  of  1%  on  the  ore."  W.  H. 
Ballantyne,  patent  lawyer  for  Minerals  Separation,  testified,  in  the 
Hyde  suit,  that  "an  ideal  standard  for  the  agitation-froth  process  is 
1 J  to  2  Ib.  oil  per  ton  of  ore. ' '  Much  less  is  used  now  in  the  big  mills 
of  the  copper  mining  companies. 

The  process  was  first  introduced  on  a  working  scale  in  the  Central 
mill  of  the  Sulphide  Corporation,  at  Broken  Hill,  as  already  men- 
tioned. Two  years  later,  in  1907,  it  was  adopted  by  the  Zinc  Corpora- 
tion, to  be  discarded  during  1909  in  favor  of  the  Elmore  vacuum 
process,  and  to  be  restored  again  to  favor  in  1911.  See  Fig.  9. 

The  next  important  application  was  made  in  1912  at  the  Braden 
Copper  mine,  in  Chile,  where  a  200-ton  plant  was  erected.  The  ex- 
traction of  copper  (as  concentrate)  was  80  to  85%.  But  when  a 
larger  mill  of  two  600-ton  units  was  built  the  recovery  became  poor, 
being  no  better  than  it  had  been  in  the  old  water-concentration  mill, 
namely,  about  65%.  Whereupon  the  oil  was  added  to  the  ore  in  the 
tube-mill  and  the  extraction  improved  at  once.  The  mill  has  now  been 
enlarged  to  seven  600-ton  units,  treating  3500  tons  per  day.44  The 
extraction  last  year  was  77  per  cent. 

In  February  1915  the  Anaconda  Copper  Mining  Company  took  a 
license  from  Minerals  Separation,  and  at  that  time  also  the  Inspira- 
tion Consolidated  Copper  Company  made  an  agreement  for  the  same 
purpose.  Both  companies  built  large  mills  for  the  operation  of  the 
process  during  last  year.45  The  Anaconda  now  treats  12,000  tons  and 
the  Inspiration  8000  tons  of  ore  daily  by  flotation. 

The  first  mining  company  in  America  to  ignore  the  Minerals 
Separation  patents  was  the  Butte  &  Superior,  in  Montana.  Under 
the  technical  guidance  of  James  M.  Hyde,  this  company  built  a  150-ton 


44'The  Braden  Mill.'    Mining  and  Scientific  Press,  December  18,  1915. 

^'Flotation  at  the  Inspiration  Mine,  Arizona.'  Mining  and  Scientific 
Press,  July  3,  1915.  Also  'Flotation  at  the  Washoe  Reduction  Works, 
Anaconda.'  By  E.  P.  Mathewson.  M.  &  8.  P.,  August  28,  1915. 


32 


THE  FLOTATION   PROCESS 


unit  in  their  mill  during  1912.     This  provoked  the  first  test  case,46 
which  is  now  before  the  Supreme  Court  of  the  United  States. 

Other  companies  charged  with  infringement  are  the  Utah  Copper, 
Nevada  Consolidated,  Magma  Copper,  and  the  Miami.    The  first  three 


FIG.    9.      THE    FROTHING    PROCESS    IN    THE    CENTRAL    MILL. 


use  the  Janney  machine  and  the  last  one  the  Callow  pneumatic 
launder.  In  each  case  it  is  stated  that  the  Minerals  Separation  ma- 
chine— in  which  violent  agitation  is  effected  by  blade-impellers — was 
tried  first  and  then  discarded  as  ineffective.  The  pneumatic  flotation 
plant  at  Miami  was  commenced  in  August  1914  and  remodeled  in  the 
early  part  of  1915.  Suit  for  infringement  was  brought  at  once  by 
Minerals  Separation,  the  trial  commencing  on  March  29  and  ending 
on  May  27,  1915.  The  decision  of  the  Court  is  not  yet  known. 


"Minerals    Separation,    Limited,    and    Minerals    Separation    American 
Syndicate,  Limited,  v.  James  M.  Hyde. 


THE   FLOTATION   PROCESS  33 

As  applied  at  Miami  the  flotation  process  is  simplified  by  the  use  of 
a  launder  having  a  canvas  bottom  through  which  air  is  forced  under 
pressure.  This  gives  the  gas  required  for  the  generation  of  bubbles 
in  a  pulp  previously  modified  by  the  addition  of  oil,  which  is  mixed 
with  the  ore  while  being  pumped  into  a  Paehuca  tank,  or  Brown 
agitator,  where  it  undergoes  further  emulsification  before  entering 
the  Callow  launder  constituting  the  flotation-cell.  It  is  claimed  that 
the  froth  produced  in  this  way  is  different  from  that  made  in  the 
mechanical  mixer  of  the  Minerals  Separation  machine.  In  the  one 
case,  according  to  E.  C.  Canby,  the  froth  consists  of  a  mass  of  delicate, 
fragile,  and  evanescent  bubbles,  which  rise  to  the  surface  in  rapid 
succession  and  maintain  a  froth  only  because  they  are  being  generated 
slightly  faster  than  they  break,  so  that  the  uppermost  layer  overflows, 
with  its  burden  of  mineral,  over  the  lip  of  the  vessel.  In  the  other 
case  the  froth  is  said  to  be  " thick,  coherent,  and  persistent,'*  as 
Mr.  Picard  phrased  it.  ' '  It  appears  as  if  the  minerals  were  protecting 
the  tender  air-bubble  like  an  armor,  and  instead  of  destroying  it,  were 
actually  guarding  it.  The  froth  has  a  long  life.  I  have  myself  seen 
a  froth  standing  for  24  hours  without  the  least  change  having  taken 
place/'  So  testified  Dr.  Adolf  Liebmann.  Mr.  Ballantyne  stated 
that  this  agitation-froth  of  the  Minerals  Separation  machine  was  so 
dense  that  it  would  support  a  spade.  Mr.  Canby  showed  that  the  air- 
froth  of  the  Callow  machine  would  not  support  a  match -stem. 

From  the  foregoing  summary  it  is  clear  that  three  processes  are 
covered  by  the  general  term  'flotation,'  and  that  to  clarify  the  dis- 
cussion of  the  subject  it  will  be  well  to  distinguish  between 

1.  Film-suspension,  as  in  the  Wood  and  Macquisten  methods. 

2.  Oil-flotation,  as  in  the  Robson  and  Elmore  bulk-oil  methods. 

3.  Bubble-levitation,  as  in  the  Elmore  vacuum,  Delprat,  Froment, 
and  Sulman-Picard  methods.    - 

The  third  class  can  be  further  sub-divided  according  as  carbon 
dioxide  or  air  is  the  principal  gas  utilized  for  making  bubbles. 

Finally,  the  air-bubble  methods  can  be  classified  according  to  the 
way  in  which  the  air  is  introduced : 

(1)  From  the  bottom  of  the  vessel,  as  in  the  Callow  and  Owen 
cells. 

(2)  By  being  entrained  or  dragged  into  the  pulp  by  the  beating 
of  paddles  or  some  other -form  of  impeller,  as  in  the  Gabbett  and 
Hoover  mixers. 

(3)  By  escape  from  solution  in  water,  as  in  the  Elmore  vacuum 
machine  and  the  Norris  apparatus. 


34  THE   FLOTATION   PROCESS 

It  remains  to  emphasize  the  fact  that  from  the  high  ratio  of  3  tons 
of  oil  per  ton  of  ore,  the  proportion  of  oil  used  in  flotation  has  de- 
creased, by  reason  of  the  recognition  of  the  part  played  by  air,  to 
one-third  of  a  pound  per  ton  of  ore ;  that  is,  one  eighteen-thousandths 
of  the  quantity  used  by  Eobson.  Concurrently  the  acid  used  has 
decreased  to  a  minus  quantity,  namely,  alkalinity. 

THE  PATENTS.  This  is  the  part  of  the  subject  of  which  we  have 
heard  the  most;  indeed,  until  recently  the  literature  of  the  flotation 
process  was  closely  identified  with  the  records  of  patent  litigation. 
That  is  why  the  scientific  principles  are  as  yet  so  little  under- 
stood and  the  technology  of  the  process  has  made  such  scanty 
progress.  The  aim  of  a  patent  specification  is  to  disclose  just  enough 
to  prove  originality.  In  many  cases  this  has  been  done  to  the  apparent 
satisfaction  of  the  Examiner  of  Patents  without  conveying  all  the 
facts  essential  to  a  clear  understanding  of  the  operations  involved. 
The  description  given  in  a  modern  patent  is  cryptic ;  it  is  couched  in  a 
quasi-legal  jargon  that  assists  obfuscation.  I  refer  to  processes  only, 
for  the  disputes  over  flotation  patents  have  arisen  over  methods,  not 
machines.  The  apparatus  required  had  already  been  used  in  other 
branches  of  wet  metallurgy,  so  that  we  have  been  spared  one  source 
of  trouble,  at  least. 

The  litigation,  which  is  now  a  serious  obstacle  to  the  free  develop- 
ment of  the  process,  has  arisen  largely  from  confusion  of  ideas  as  to 
the  underlying  causes  of  flotation.  The  patentees  did  not  understand 
the  phenomena  with  which  they  played.  Those  to  whom  they  sold 
their  patents  knew  even  less.  The  interpretations  of  attorneys  and 
judges  have  elucidated  the  law  but  confused  the  physics.  No  clear 
adjudication  of  rights  is  possible  so  long  as  claims  and  counter-claims 
are  based  on  an  ignorance  of  the  rationale  of  the  process. 

As  the  flotation  process  of  today  is  essentially  that  of  making  a 
mineral-buoying  froth  in  modified  water,  it  is  not  necessary  for  me  to 
make  further  reference  to  the  patents  granted  for  the  use  of  purely 
surface-tension  effects.  It  would  seem  permissible  also  to  omit  further 
consideration  of  the  bulk-oil  methods,  but,  as  a  matter  of  fact,  none 
of  these  operated  without  the  aid  of  air,  although  the  patentees  were 
quite  unaware  of  it,  and  it  was  from  these  bulk-oil  methods  that  the 
frothing  process  was  developed  fortuitously. 

The  first  patent  for  the  use  of  oily  substances  and  coal-tar  products 
in  the  concentration  of  ores  was  that  granted  to  William  Haynes,  an 
Englishman,  in  1860 ;  but  this  is  now  only  of  academic  interest.  Next 
comes  the  patent  of  Carrie  J.  Everson,  dated  August  24,  1886,  the 


THE   FLOTATION   PROCESS  35 

application  having  been  filed  on  August  29,  1885.20  The  Everson 
patent  refers  to  the  selective  action  of  oil  for  "metallic  substances" 
and  the  increase  caused  in  that  selectiveness  by  the  addition  of  acid. 
The  pulp  is  stirred  so  as  to  bring  "the  mineral"  in  contact  with  the 
oil  and  acid,  producing  a  "stiff  mass."  The  use  of  "about  a  barrel 
of  oil  to  the  ton  of  ore"  is  mentioned,  indicating  a  ratio  of  about 
17%.  Other  statements  indicate  that  she  used  as  little  as  5%  of  oil 
per  ton  of  ore.  The  separation  of  the  oiled  mineral  from  the  unoiled 
gangue  is  described  thus :  "  In  practice,  the  concentrate,  after  thorough 
agitation  of  the  mass  and  detachment  of  the  sand,  will  in  this  case  be 
preferably  removed  by  means  of  a  constant  overflow  of  water  from  a 
washing-out  vessel,  by  which  overflow  the  concentrate  will  be  floated 
off."  These  last  words  constitute  the  only  direct  reference  to  the 
floating  of  the  concentrate. 

A  great  deal  more  has  been  read  into  this  patent  than  could  ever 
have  been  in  the  mind  of  the  patentee.  It  is  difficult  to  read  her  de- 
scription without  cocking  one  eye  at  the  present  practice  of  flotation, 
whereby  some  of  Mrs.  Everson 's  phrasing  is  given  a  significance  to 
which  it  had  no  possible  claim  30  years  ago.  The  proportion  of  oil 
used,  even  the  maximum,  would  not  suffice  for  the  operation  she  had 
in  mind,  namely,  the  floating  of  the  heavy  sulphides  by  direct  aid 
of  the  buoyancy  of  oil.  Her  maximum  proportion  of  oil  represents  a 
mere  fraction  of  the  quantity  required  for  this  operation.  She  dis- 
closed no  notion  of  the  assistance  to  be  obtained  from  air,  in  the  form 
of  bubbles,  although,  of  course,  this  was  her  principal  flotative  agent. 
The  process  described  by  her  is  quite  impracticable  on  a  large  scale, 
and  it  never  was  operated  save  in  a  crude  experimental  way.  Never- 
theless the  exigencies  of  patent  litigation  have  caused  the  opponents 
of  Minerals  Separation  to  idealize  both  Mrs.  Everson  and  her  metal- 
lurgical adventure,  as  they  have  also  created  a  romantic  story  of  the 
supposed  epoch-making  discovery.  She  is  represented  as  a  school- 
teacher, a  Miss  Everson,  who,  as  the  sister  of  an  assayer,  washed  some 
greasy  ore-sacks  and  saw  the  sulphides  floating  on  the  contaminated 
water.  Even  the  idea  of  agitation  was  suggested  by  the  activity  of  her 
hands  in  the  wash-tub.  Therefore  "it  only  required  the  customary 
acuteness  of  observation  of  the  "Western  lady  school-teacher  to  grasp 
the  essential  facts  of  sulphide  flotation."21  This  is  pretty,  but  not 
scientific.  The  "essential  facts"  are  a  bit  too  slippery  to  be  grasped 


2oThe  date  of  application  is  the  more  important,  as  being  the  one  from 
which  priority  of  invention  is  measured. 

2i'Concentrating  Ores  by  Flotation.'    Page  5. 


36  THE  FLOTATION   PROCESS 

firmly  even  today.  In  thinking  acid  necessary,  she  was  wrong.  It  is 
known  now  not  to  be  an  essential.  Even  the  use  of  oil  as  a  direct 
means  of  buoyancy  has  receded  into  the  background;  if  she  had  un- 
derstood the  rationale  of  her  own  operations  she  would  have  known 
that  it  was  not  so  much  the  selective  adhesion  of  the  oil  to  the  mineral 
particles  that  gave  her  the  requisite  buoyancy  as  the  greater  selective- 
ness  of  the  air  bubbles  made  by  agitation  in  water  modified  by  the  oil. 
Carrie  Jane  Everson  had  no  idea  of  the  frothing  process.  Her  methods 
may  have  involved  bubble-levitation,  but  she  did  not  know  it,  and  her 
description  would  not  suggest  it  to  anyone  not  versed  in  much  later 
knowledge.  The  effort  to  feature  this  lady  as  the  inventor  of  the 
frothing  process  cannot  commend  itself  to  an  unprejudiced  student 
of  the  subject. 

It  is  interesting  to  add  that  the  "Miss  Everson "  of  the  story  was 
really  a  Mrs.  Everson;  the  wife  of  a  Chicago  doctor;  she  was  not  a 
school-teacher ;  her  brother  was  not  an  assayer ;  and  there  is  no  reason 
for  regarding  the  story  of  the  ore-sacks  as  anything  more  than  the 
fiction  of  an  irresponsible  scribe.22  Mrs.  Everson  died  at  San  Anselmo, 
California,  on  November  3,  1914.23 

Next  comes  the  British  patent  of  January  8,  1894,  granted  to 
George  Robson,24  an  Englishman,  who  did  his  experimental  work  at 
the  same  place  and  on 'the  same  ores  as  the  Elmore  brothers,  at  the 
Glasdir  mine,  near  Dolgelly,  in  Wales.  He  disclaimed  "the  use  of 
acids  or  salts  and  also  the  method  of  washing  away  the  gangue  with 
water,"  effecting  "the  separation  of  the  metallic  matter  by  the  mix- 
ture of  oils  alone."  He  does  not  specify  the  quantity  of  oil,  but  I 
am  informed  that  it  was  in  the  ratio  of  3:1,  three  tons  of  oil  to  one 
of  ore.  This  was  true  bulk-oil  flotation  and  it  proved  an  abject 
failure. 

Then  came  Francis  Edward  Elmore,  on  April  10,  1899,  duplicating 
his  British  patent  of  October  18,  1898.  His  method  has  been  described 
already.  It  only  remains  to  say  that  in  so  far  as  this  method  proved 
more  practicable  than  that  of  Robson,  the  result  was  due  to  the  fact 
that  the  Elmore  brothers  were  capable  engineers  and  therefore  de- 
signed a  more  suitable  plant.  The  patent  ignored  the  use  of  air ;  the 
intention  was  not  to  emulsify  the  oil  and  not  to  aerate  the  pulp,  but 
this  theoretical  condition  was  never  fulfilled,  as  is  clear  from  the  fact 
that  the  flotative  action  was  150%  more  than  that  calculable  from  the 


22ln  the  Financial  Times,  March  3,  1902. 

23'The  Everson  Myth.'    Mining  and  Scientific  Press,  January  15,  1916. 

2<His  American  patent  is  dated  January  19,  1897. 


THE   FLOTATION   PROCESS  37 

difference  of  specific  gravity  between  the  oil  and  the  water.  On  Janu- 
ary 3,  1903,  A.  Stanley  Elmore  took  out  a  British  patent  for  an  ap- 
paratus for  excluding  the  air  during  the  operation.  He  effected  his 
purpose  by  sealing  all  the  open  vessels  with  a  ring  or  surface  of  oil; 
from  which  it  is  evident  that  at  that  time  he  and  his  brother  en- 
deavored to  base  their  method  wholly  on  bulk-oil  flotation. 

In  January  1902,  Charles  V.  Potter,  an  Australian,  obtained  a 
British  patent  for  the  flotation  of  sulphides  in  a  hot  acid  solution. 
He  used  a  stirrer,  and  he  claimed  that  the  solution  would  "  react  on 
the  soluble  sulphides  present  to  form  bubbles  of  sulphuretted  hydro- 
gen on  the  ore  particles  and  thereby  raise  them  to  the  surface."25 

In  November  of  the  same  year,  1902,  Gruillaume  D.  Delprat,  the 
manager  of  the  Broken  Hill  Proprietary  mine,  applied  for  a  similar 
patent,  except  that  he  used  salt-cake  instead  of  sulphuric  acid.  Liti- 
gation ensued,  followed  by  a  compromise,  eliminating  Potter.  In  later 
patents  both  Potter  and  Delprat  introduced  the  use  of  oil,  finding  it 
beneficial. 

In  his  first  American  patent,  No.  735,071,  filed  on  January  2,  1903, 
Delprat  states  that  the  process  ' '  depends  upon  the  ore  particles  being 
attacked  by  the  acid  to  form  a  gas.  Each  ore  particle  so  attacked  will 
have  a  bubble  or  bubbles  of  gas  adhering  to  it,  by  means  of  which  it  will 
be  floated  and  can  be  skimmed  or  floated  off  the  solution."  (''Ore 
particles"  means  blende  and  galena  at  Broken  Hill.)  Here  is  a 
pretty  good  recognition  of  bubble-levitation,  only  he  supposed  the 
sulphides,  not  the  gangue,  to  be  attacked  by  the  acid.  In  another 
place  he  says  specifically:  "The  sulphides  in  the  ore  are  rapidly 
attacked  by  the  acid  and  gas-bubbles  formed  on  them,  that  quickly 
carry  them  to  the  surface."  In  this  patent  he  claimed  the  use  of 
nitric  acid  and  a  suitable  nitrate,  such  as  sodium  nitrate,  the  latter 
being  intended  "to  increase  the  specific  gravity  of  the  bath."  What 
reaction  was  to  follow  between  the  sulphides  and  the  dilute  nitric  acid 
is  not  clear.  It  has  been  recorded28  that  in  the  early  days  of  the 
Potter-Delprat  methods  it  was  supposed  that  the  acid  liberated  hydro- 
gen sulphide  from  the  sulphides,  when  sulphuric  acid  was  used,  with- 
out attacking  the  gangue.  Those  who  first  scouted  this  idea  suggested 
that  carbon  dioxide  was  generated  by  decomposition  of  a  carbonate 
coating  on  the  sulphides,  due  to  weathering  of  the  ore,  arguing  there- 
from that  it  was  necessary  for  the  gas  to  be  produced  at  the  surface  of 


25U.  S.  patent  No.  776,145.    Claim  3. 

26'The  Physics  of  Ore  Flotation.'    By  J.  Swinburne  and  G.  Rudorf.    Mining 
and  Scientific  Press,  February  24,  1906. 


38 


THE  FLOTATION   PROCESS 


the  sulphide  particles  themselves.    All  of  these  explanations27  are  now 
on  the  scrap-heap  of  discarded  theories. 

These  patents  of  Potter  and  Delprat  have  been  labelled  variously 


Lead  Baffle  Plate-. 


Pocket  for  catching 
stones,  bolts  etc.  —,^ 


Metal  secrt.  — - 

4'D/am.  — 
FIG.  10.      THE  POTTER  APPARATUS. 


under  'acid-flotation'  and  'surface  tension'  methods.  Delp rat's  ap- 
paratus does  indeed  suggest  a  process  of  the  Bradford  or  Wood  type, 
but,  of  course,  both  he  and  Potter  depended  for  their  results  on  the 


27 in  his  book  Mr.  Hoover  states  (page  13,  second  edition)  that  Goyder  & 
Laughton,  in  their  patent  of  July  31,  1903,  "were  the  first  to  disclose  the 


THE   FLOTATION   PROCESS  39 

liberation  of  carbon-dioxide  gas  from  the  gangue,  which,  at  Broken 
Hill,  contains  a  large  proportion  of  carbonates,  notably  calcite,  sid- 
erite,  and  rhodocrosite.  From  any  of  these  a  hot  sulphuric-acid  solu- 
tion would  release  the  gas  that  promptly  attached  itself  to  the  metallic 
surfaces  of  the  galena  and  blende. 

Meanwhile  Alcide  Froment,  in  Italy,  had  got  hold  of  the  bubble 
idea,  .which  is  the  real  basis  of  the  flotation  process  as  it  is  understood 
today.  He  invented  his  method  in  1901  and  filed  his  claim  for  a 
British  patent  on  June  9,  1902.  This  patent  was  duplicated  in  Italy, 
but  not  in  the  United  States.  The  fact  last  mentioned  is  important. 
Froment  claimed  that  his  process  was  "a  modification  of  what  is 
known  as  the  oil  process  of  ore  concentration, "  meaning  that  of 
Elmore,  for  the  bulk-oil  method  had  been  tried  at  the  Traversella 
mine,  in  Italy,  where  Froment  was  engaged  as  an  engineer.  His  plan 
was  to  generate  bubbles  of  gas  by  the  reaction  between  sulphuric  acid 
and  the  carbonates  in  the  gangue,  adding  limestone  when  the  ore  did 
not  contain  enough  carbonate.  He  argues  that  "if  a  gas  of  any  kind 
is  liberated  in  the  mass,  the  bubbles  of  the  gas  become  coated  with  an 
envelope  of  sulphides  and  thus  rise  readily  to  the  surface  of  the  liquid 
where  they  form  a  kind  of  metallic  magma. ' '  It  will  be  noted  that  he 
says  "gas  of  any  kind."  As  the  children  say,  in  a  familiar  game,  he 
was  "very  warm"  just  then,  for  he  had  only  to  invoke  the  aid  of  air 
to  have  described  the  essential  principle  of  the  later  phase  of  flota- 
tion. He  also  states  that  the  sulphide  particles  when  ' '  moistened  by  a 
fatty  substance"  have  a  tendency  "to  unite  as  spherules  and  to  float 
upon  the  surface  of  the  water. ' '  His  brief  description  closes  with  -the 
statement  that  "the  rapidity  of  the  formation  of  the  spherules  and 
their  ascension  is  in  direct  ratio  to  the  quantity  of  gas  produced  in  a 
given  time."  As  to  the  oil,  the  only  mention  of  quantity  is  made  in 
describing  a  test-tube  experiment  in  which  he  uses  "a  thin  layer  of 
oil."  This  phrase  has  been  variously  interpreted,  according  to  the 
exigencies  of  litigation,  but  it  refers  obviously  to  a  minute  proportion. 


principle  governing  Potter's  and  Delprat's  acid-flotation  process,  namely,  that 
the  action  of  the  acid  on  the  ore  generated  gas-bubbles  to  which  the  sulphide 
particles  attach  themselves,  and  were  floated  to  the  surface."  What  they 
said  was  that  "the  physico-chemical  action  develops  the  formation  of  gas- 
bubbles  adhering  to  particles  of  certain  of  the  finely-divided  minerals  and 
causing  such  particles  of  certain  minerals  to  rise  to  or  near  the  surface  of 
the  solution."  But  this  does  not  make  it  clear  that  the  bubbles  are  obtained 
by  the  decomposition  of  the  carbonates  in  the  gangue;  it  is  ^rnore  nearly 
compatible  with  Delprat's  idea  that  they  were  generated  by  the  action  of  the 
acid  on  the  sulphides  themselves. 


40  THE  FLOTATION   PROCESS 

In  the  directions  given  by  him  to  the  Minerals  Separation  people  when 
they  bought  his  patent  rights  on  November  17,  1903,  he  specified  1% 
of  mineral  engine-oil  for  ore  containing  up  to  5%  of  metal,  1J  of  oil 
for  ore  containing  10%,  and  so  on,  up  to  ores  containing  50%  of 
metallic  lead,  which  would  require  3J%  of  oil.  As  oil  notation  was 
understood  at  that  time,  this  marked  a  great  reduction  in  the  pro- 
portion of  oil.  However,  the  more  interesting  point  is  Froment's 
failure  to  perceive  the  possibility  of  using  air  as  the  gas  for  making 
his  bubbles.  He  depended  upon  chemical  action  to  furnish  him  with 
the  necessary  gas.  Nevertheless  Froment  deserves  a  high  place  in  the 
roll  of  flotation  pioneers,  for  he  made  an  important  step  forward.  He 
furnished  the  link  between  bulk-oil  and  air-froth  flotation. 

The  next  chapter  in  the  story  marks  a  retrogression.  Under  date 
of  November  28,  1902,  Arthur  E.  Cattermole  obtained  British  patents 
No.  26,295  and  26,296,  both  of  which  were  acquired  by  John  Ballot 
and  associates  in  December  1902,  preparatory  to  the  formation  of  the 
company — Minerals  Separation,  Ltd. — organized  to  exploit  them. 
In  August  1903  Cattermole  revised  and  amplified  his  previous  claims 
in  British  patent  No.  18,589,  which  was  duplicated  in  the  United 
States  under  date  of  September  28,  1903,  as  No.  777,273.  This  last 
is  the  principal  patent  covering  the  so-called  granulation  process. 

Cattermole  prefaces  his  description  by  reference  to  the  selectiveness 
•of  oil,  when  emulsified,  for  sulphide  particles,  such  selective  action 
being  intensified  by  the  acidulation  of  the  water.  He  then  proceeds 
to  say  that  if  the  mixture  be  thoroughly  agitated,  there  is  a  tendency 
for  the  metalliferous  particles,  now  coated  with  oil,  to  adhere  together, 
forming  granules28  that  sink  and  are  readily  separated  from  the 
lighter  gangue  by  an  up-current  of  water.  In  his  description  of  the 
operation  he  says  that  ' '  the  granules,  with  a  certain  amount  of  heavy 
sands,  sink  to  the  bottom  and  are  discharged  [see  Fig.  11]  through 
a  pipe  G1  into  the  vessel  A5,  while  the  lighter  sands  are  carried  away 
by  the  upward  current  and  discharged  through  outlet  G2  to  a  light- 
sands  tank  J."  In  the  drawing,  A1,  A2,  A3,  A4,  A5,  and  A6  are  mixing 
vessels ;  G  and  K  are  classifiers ;  E  is  a  tank  containing  oil  emulsion. 
He  refers  to  the  quantity  of  oil  several  times  in  vague  terms,  explain- 
ing, however,  that  it  should  be  "insufficient  to  materially  lessen  the 
specific  gravity  of  the  metalliferous  mineral  particles. "  Finally,  he 
specifies  the  proportion  as  "usually  an  amount  of  oil  varying  from 
4%  to  6%  of  the  weight  of  metalliferous  mineral  matter  present  in 
the  ore."  t  This  can  be  interpreted  variously;  if  it  refers  to  the  sul- 

28The  'granules'  may  be  contrasted  with  Froment's  'spherules.' 


THE   FLOTATION   PROCESS 


41 


phides  to  be  concentrated,  then  an  ore  containing  20%  blende  would 
require  from  0.8  to  1.2%  of  oil,  equivalent  to  from  16  to  24  Ib.  oil  per 
ton  of  ore.  On  the  other  hand  a  2%  chalcocite  ore  would  need  only 
1.6  to  2.4  Ib.  of  oil  per  ton  of  ore,  which  is  as  little  as  is  now  used. 

This  Cattermole  process  was  the  subject  of  lengthy  experiment  in 
the  London  laboratory  of  the  Minerals  Separation  company,  where  all 


No,  763,259.  PATENTED  JUNE  21,  1904. 

A.  E.  CATTERMOLE. 
CLASSIFICATION  OF  THE  METALLIC  CONSTITUENTS  OF  ORES. 

APPLICATION  PILED  SEPT.  29.  1903. 
10  MODEL. 


FIG.  11.     THE  CATTEBMOLE  PATENT. 


42  THE  FLOTATION   PROCESS 

sorts  of  variations  in  temperature,  acidification,  oiling,  and  mixing 
were  tried  by  Arthur  H.  Higgins  under  directions  from  H.  L.  Sulman 
and  H.  F.  K.  Picard.  It  was  not  until  March  1905,  that  is,  nearly 
2J  years  subsequent  to  the  patenting  of  the  Cattermole  method,  that 
it  was  found  advisable  to  float  the  'granules'  rather  than  sink  them, 
whereupon  ensued  "the  startling  discovery  of  the  agitation-froth 
process,"  as  "W.  H.  Ballantyne  has  described  it.  A  similar  discovery 
was  made  contemporaneously  at  Broken  Hill,  but  there,  according  to 
James  Hebbard,  it  was  not  so  ' '  startling ; "  it  was  the  result  of  strenu- 
ous efforts  to  make  a  workable  process  out  of  the  impracticable 
method  devised  by  Cattermole.  See  Fig.  12  and  14. 

This  'discovery'  led  to  Minerals  Separation's  basic  patent  U.  S. 
No.  835,120,  of  May  29,  1905,  which  duplicated  the  British  patent 
No.  7803  of  April  12,  1905,  taken  out  in  the  names  of  H.  L.  Sulman, 
H.  F.  K.  Picard,  and  John  Ballot.  In  this  patent  the  aid  of  chemically- 
generated  gas  is  discarded  definitely,  in  favor  of  air-bubbles.  This 
seems  to  me  a  matter  of  far  greater  importance  than  the  reduction 
in  the  proportion  of  oil.  The  patentees  say :  "  It  is  to  be  understood 
that  the  object  of  using  acid  in  the  pulp  according  to  this  invention  is 
not  to  bring  about  the  generation  of  gas  for  the  purpose  of  flotation 
thereby,  and  the  proportion  of  acid  used  is  insufficient  to  cause 
chemical  action  in  the  metallif erous  minerals  present. ' '  This  differen- 
tiates the  method  from  those  of  Potter,  Delprat,  Froment,  and  De 
Bavay,  the  addition  of  acid  being  therefore  presumably  to  assist  the 
selective  oiling  of  the  sulphides.  The  patentees  also  state  that ' '  a  large 
proportion  of  the  mineral  present  rises  to  the  surface  in  the  form  of  a 
froth  or  scum  which  has  derived  its  power  of  flotation  mainly  from  the 
inclusion  of  air-bubbles  introduced  into  the  mass  by  the  agitation, 
such  bubbles  or  air-films  adhering  only  to  the  mineral  particles  which 
are  coated  with  oleic  acid."  The  last  clause  had  better  have  been 
omitted,  for  it  is  only  conjecture,  as  to  the  truth  of  which  there  is 
room  for  plenty  of  doubt,  but  the  clear  description  of  air  as  the  main 
agent  of  flotation  is  most  important — far  more  important  as  regards 
the  rationale  of  the  process,  than  the  diminution  in  the  proportion  of 
oil. 

As  to  this,  it  is  stated  that  if  the  proportion  of  oil  mentioned  in 
the  previous  Cattermole  patents  "be  considerably  reduced — say  to 
a  fraction  of  1%  on  the  ore — granulation  ceases  to  take  place,  and 
after  vigorous  agitation  there  is  a  tendency  for  a  part  of  the  oil- 
coated  metalliferous  matter  to  rise  to  the  surface  of  the  pulp  in  the 
form  of  a  froth  or  scum."  One  per  cent  on  the  ore  is  equal  to  20  Ib. 


THE   FLOTATION   PROCESS 


43 


of  oil  per  ton;  a  'fraction'  of  1%  is  anything  between  20  and  0 
pounds  per  ton.  In  enforcing  the  right  to  the  collection  of  royalties, 
the  Minerals  Separation  company  has  rested  its  claim  mainly  on 
the  reduction  of  oil,  claiming  that  it  produces  a  series  of  phenomena 
quite  different  from  any  of  the  other  methods  employing  larger  pro- 
portions of  oil,  and,  concurrently,  insisting  that  such  superior  effects 
as  are  produced  by  the  use  of  the  reduced  quantity  of  oil  are  un- 

Uo.  835,120.  PATENTED  NOV.  6,  1906. 

H.  L.  SULMAN,  H.  F.  KIRKPATRICK-PICARD  &  J.  BALLOT. 

ORE  CONCENTRATION. 

APPLICATION  FILED  MAT  29. 1905. 

2  SHEETS-WEST  2. 


PlG.  12.   THE  CHIEF  MINERALS  SEPARATION  PATENT. 


44  THE   FLOTATION   PROCESS 

obtainable  when  the  larger  proportions  of  oil  are  used.  Thereupon, 
of  course,  it  has  been  claimed,  by  those  desiring  to  ignore  the  Minerals 
Separation  basic  patent,  that  neither  the  Cattermole  nor  the  Froment 
methods  demanded  a  quantity  of  oil  notably  larger,  for  the  minima 
prescribed  by  these  earlier  inventors  come  under  20  Ib.  of  oil  per 
ton  of  ore.  However,  this  matter  is  still  sub  judice,  so  it  is  best  let 
alone  for  the  present. 

Between  the  Froment  patent  of  1902  and  the  Sulman-Picard 
Ballot  patent  of  1905  comes  the  Kirby  patent  U.  S.  No.  809,959  of 
December  14,  1903,  granted  on  January  16,  1906.  This  is  interesting 
as  specifying  gentle  agitation  and  the  use  of  a  gas,  making  it  possible 
to  use  thin  oils  instead  of  the  viscous  oils  of  the  prior  (Elmore)  art. 
The  claim  is  made  that  "the  injection  of  gas,  preferably  air,  into  the 
mass,  assists  in  the  flotation  of  the  hydrocarbon-coated  particles/' 
The  mention  of  air,  as  an  assistant  flotative  agent,  is  more  important 
than  the  reference  to  the  kind  of  oil. 

The  actual  part  played  by  the  oil  has  been  misapprehended  from 
the  very  first,  the  earlier  investigators  using  not  enough  to  produce 
bulk-oil  flotation,  while  the  later  metallurgists  have  employed  much 
more  than  was  needed  for  bubble-levitation.  The  relative  importance 
of  the  part  played  by  air  was  persistently  ignored  until  a  late  date 
and  even  then  it  was  under-estimated.  It  is  interesting  to  note  that 
the  two  first  patents  in  which  air  was  specified  as  a  gas  suitable  for 
flotative  effects  were  those  of  F.  E.  Elmore  and  the  firm  of  Sulman 
&  Picard.  Francis  E.  Elmore  obtained  a  British  patent  for  his 
vacuum-oil  method  under  date  of  August  16,  1904,  and  duplicated  it 
in  the  United  States  as  No.  826,411  of  July  10,  1905.  Sulman  & 
Picard  obtained  a  British  patent  for  their  perforated-coil  patent 
under  date  of  September  22,  1903,  duplicating  it  in  the  United 
States  as  No.  793,808  of  October  5,  1903. 

The  Sulman  &  Picard  patent  just  mentioned  has  been  claimed  by 
the  Miami  Copper  Company  as  the  one  covering  their  operations  with 
the  Callow  pneumatic  cell.29  In  No.  793,808  the  inventors  "utilize 
the  power  which  is  possessed  by  films  or  bubbles  of  air  or  other  gas' 
of  attaching  themselves  to  solid  particles  moistened  by  oil  or  the 
like/'  They  also  state  that  they  add  oil  "in  quantity  insufficient  to 
raise  the  oiled  mineral  by  virtue  of  the  flotation  power  of  the  oil  alone. 
A  suitable  gas  is  generated  in  or  introduced  into  the  mixture,  such 
as  air,  carbonic-acid  gas,  sulphuretted  hydrogen,  or  the  like.  For 
example,  bicarbonates  or  carbonates,  either  soluble  or  insoluble  in 

2»Note  the  sloping  launder-like  vessel  used  by  both.    See  Fig.  15  and  33. 


THE   FLOTATION    PROCESS 


45 


water  (preferably  the  latter)  or  easily  decomposable  sulphides  and 
the  like  may  be  used  with  acid  solution."  Thus  they  lessen  the 
emphasis  on  air  as  the  prime  agent.  The  description  also  refers  to 
the  oiled  metalliferous  particles  as  "attaching  to  themselves,  with 
a  greater  comparative  strength  than  the  gangue  particles,  the  films  or 


No.  873,586  PATENTED  DEC.  10,  1907. 

D.  H.  NORRIS. 

APPARATUS  FOR  SEPARATING  THE  METALLIC  PARTICLES  OF  ORES  FROM 
THE  ROCKY  CONSTITDENTS  THEREOF. 

APPLICATION  FILED  AUG.  7.  1907 


Jrwcntor 

JJudkyRTfarrti. 


FIG.    13.      THE   NOBRIS  PATENT. 


46  THE  FLOTATION   PROCESS 

bubbles  of  gas  which  exist  in  the  mass  and  are  thus  raised  to  the 
surface  of  the  liquor  by  gaseous  flotation."  Yet  we  are  told  that 
the  metallurgists  who  prepared  this  excellent  description  of  the 
bubble-levitation  method  made  "a  startling  discovery"  of  the  froth- 
ing process  eighteen  months  later.  This  U.  S.  patent  793.808  is  more 
than  a  year  junior  to  Froment's  British  patent,  and  contains  an  echo 
of  it  in  the  introductory  announcement. 

Elmore's  vacuum-oil  process  marked  another  inadvertent  step 
toward  the  recognition  of  air  as  the  most  important  flotative  agent. 
He  utilizes  the  air  naturally  dissolved  in  water,  releasing  it  for  his 
purpose  under  a  vacuum.  The  patent  states  that  "under  a  vacuum 
or  partial  vacuum,  air  or  gases  dissolved  in  the  milling  water  are 
liberated.  These  liberated  gases  may  be  augmented  by  the  generation 
of  gases  in  the  pulp,  or  by  introduction  from  an  external  source." 
Elmore  invented  a  most  ingenious  machine  for  his  purpose.  In  so  far 
as  he  depended  upon  the  air  in  a  pulp  that  had  undergone  mixing 
with  a  quantity  of  oil  relatively  small  (as  compared  with  his  bulk-oil 
method)  he  furnished  a  notable  metallurgic  sign-post,  but  it  is 
necessary  to  remember  that  he  mixed  his  crushed  ore  in  acidulated 
water  and  that  the  acid  would  cause  the  generation  of  carbon-dioxide 
gas,  thus  explaining  his  reference  to  * '  air  or  gases. ' ' 

The  first  inventor  to  break  away  from  the  use  of  either  acid  or  oil 
and  to  make  a  clear  claim  for  air  as  his  sole  flotative  agent  is  Dudley 
H.  Norris,  in  U.  S.  No.  864,856,  under  date  of  November  19,  1907, 
also  in  No.  873,586,  of  December  10,  1907.  See  Fig.  13.  In  his 
first  patent  he  described  a  method  for  "introducing  water  containing 
air  in  solution  into  the  lower  end  of  an  open-ended  receptacle  into 
which  is  introduced  a  flowing  mixture  of  pulverized  ore  mixed  with  oil 
and  water,  thereby  exposing  said  mixture  to  the  continuous  action  of 
infinitesimally  small  nascent  bubbles  of  air."  He  does  not  specify  the 
use  of  acid  and  he  distinctly  says  that  he  does  not  wish  it  to  be  under- 
stood that  his  method  ' '  is  limited  to  the  use  of  oil,  as  the  method  can 
be  practised  successfully  without  mixing  oil  with  the  pulverized  ore 
and  water."  Incidentally,  his  method  is  worthy  of  friendly  interest, 
for  he  has  declared  his  intention  to  render  the  use  of  it  free  of  tonnage 
royalty.* 

Having  got  rid  of  acid  and  oil,  we  have  now  reached  the  point 
where  modified  water  mixed  with  the  crushed  ore  in  the  presence 
of  air  suffices  to  form  bubbles  sufficiently  lasting  to  buoy  the  metallic 
particles  to  the  surface  of  the  liquid. 


*See  page  274  of  this  book. 


THE   FLOTATION   PROCESS  47 

THE  PSYCHOLOGY.  A  potent  factor  in  the  history  of  flotation  has 
been  the  psychology  of  the  persons  concerned  in  the  invention,  improve- 
ment, and  application  of  the  process.  To  understand  the  scanty  and 
contradictory  literature  of  the  subject  it  is  necessary  to  read  between 
the  lines  with  some  knowledge  of  the  personal  equations  that  have 
rendered  the  problem  so  confusing  to  the  later  student.  For  example, 
it  is  an  interesting  fact  that  the  first  workable  method  was  that  of  the 
Elmores.  who,  however,  simply  carried  forward  the  ineffective  re- 
search of  Robson  and  Crowder,  at  the  Glasdir  mine.  The  Elmores 
knew  of  the  experiments  made  by  Robson,  more  particularly,  for 
his  simple  apparatus  was  left  on  view  at  the  mine  when  Francis 
Elmore  and  his  brother  came  there  in  1897  and  became  interested  in 
the  problem.  Next  there  is  the  fact  that  in  1902  the  Elmores  placed 
their  Australian  rights  to  the  bulk-oil  process  under  option  to 
the  group  headed  by  Messrs.  "Webster  and  Ballot,  by  whom  Messrs. 
Sulman  and  Picard  were  employed.  The  latter  were  given  every 
facility  for  becoming  completely  familiar  with  the  operations  of  the 
Elmore  process,  but  the  Australian  option  was  not  exercised,  and  the 
group  that  had  rejected  the  option  formed  the  Minerals  Separation 
company  and  proceeded  to  exploit  another  method  themselves.  Where- 
upon, not  unnaturally,  there  arose  charges  and  counter-charges  of 
bad  faith,  provoking  the  lawsuit  of  1907,30  which  decided  nothing, 
but  left  a  lot  of  ill  feeling  in  its  wake. 

The  atmosphere  amid  which  the  various  processes  were  tried  at 
Broken  Hill  is  illustrated  by  the  fact  that  in  the  course  of  a  successful, 
but  misleading,  test  of  the  Potter  method,  the  workmen  in  the  Zinc 
Corporation's  plant  made  it  a  practice  to  add  lubricating  oil  to  the 
hot-acid  solution  in  order  to  improve  the  result.  This  fact  was  not 
ascertained  until  several  years  after  the  test  had  been  finished.  At 
that  time  feeling  ran  high  between  the  various  process  companies  and 
"the  Zinc  Corporation's  experimental  work  was  subjected  to  many 
unfavorable  arguments  of  an  extremely  substantial  nature,  such  as  a 
varied  assortment  of  scrap-iron,  dropped  into  agitators,  gearing,  or 
pump -sumps."31 

In  order  to  understand  the  later  developments,  it  should  be  stated 
that  Theodore  J.  Hoover  joined  Minerals  Separation  Ltd.  as  technical 
adviser  and  general  manager  in  October  1906  and  resigned  in  De- 
cember 1910.  Unpleasant  misunderstandings  ensued.  The  first  edi- 


so'Concentrating  Ores  by  Flotation.'     Pages  46-48. 

siD.  P.  Mitchell.    'Flotation  at  Zinc  Corporation,  Ltd.'    E.  &  M.  J.,  Novem- 
ber 18,  1911. 


48  THE  FLOTATION   PROCESS 

t 

tion  of  Mr.  Hoover's  book  appeared  two  years  later,  in  December  1912. 
James  M.  Hyde  was  in  the  employ  of  the  Mexican  syndicate  organ- 
ized by  Minerals  Separation  for  one  year,  from  January  1910  to 
January  1911.  At  the  instance  of  Herbert  C.  Hoover  he  went  to 
Montana  on  an  inspection  of  the  Butte  &  Superior  mine.  Mr.  Hoover 
withdrew  from  this  business,  but  Mr.  Hyde  proceeded  to  test  the  ore 
and  erect  a  trial  flotation  plant,  in  disregard  of  the  Minerals  Sep- 
aration patents.  Suit  was  brought  against  him  by  Minerals  Separa- 
tion in  October  1911.  E.  H.  Nutter  was  engaged  by  T.  J.  Hoover  for 
Minerals  Separation  in  1910;  he  has  been  in  the  United  States  for 
that  company  since  1911,  most  of  the  time  as  its  representative  in 
San  Francisco. 

J.  M.  Callow's  American  patent  for  his  pneumatic  launder  is  No. 
1,104,755  of  July  21,  1914.  It  covers  the  same  idea  as  appears  in  T.  J. 
Hoover's  British  patent  No.  10,929  of  1910.  I  am  informed  that  Mr. 
Callow  was  unaware  of  Mr.  Hoover's  invention,  which  was  not  pat- 
ented in  this  country  and  is  now  the  property  of  the  Minerals  Sep- 
aration company.  However,  priority  of  invention  as  regards  this 
apparatus  is  a  matter  of  academic  interest  only.  R.  S.  Towne  used 
the  same  idea  earlier  than  Mr.  Callow  in  the  form  of  a  carborundum 
wheel,  the  central  hole  of  which  he  plugged,  so  that  the  wheel  served 
as  a  porous  bottom. 

No  American  application  of  the  bubble-levitation  phase  of  flotation 
to  the  concentration  of  ore  was  made  until  long  after  the  Minerals 
Separation's  basic  patent  had  been  registered.  As  previously  related, 
the  early  trials  were  made  at  Broken  Hill.  The  first  introduction  of 
this  method  in  the  United  States  occurred  six  years  after  the  date  of 
patent  No.  835,120.  It  is  claimed  by  Minerals  Separation  that  "if  the 
directions  of  the  patent  are  followed,  the  operation  of  the  process  is 
inevitable,"  yet  many  years  of  trial  and  experimentation  were  re- 
quired before  flotation  was  used  successfully  in  this  country.  The 
Utah  Copper  and  the  other  Jackling  companies  made  successful  appli- 
cation of  the  process  by  aid  of  their  own  research  and  persistent  effort. 
Up  to  1911  the  Minerals  Separation  metallurgists  thought  chalcocite 
could  not  be  treated  by  flotation,  and  said  so.  In  Mr.  Hyde's  report 
of  January  8, 1911,  given  as  an  exhibit  by  Minerals  Separation  in  their 
suit  against  Hyde,  it  is  stated  that  the  tests  carried  out  in  the  com- 
pany's London  laboratory  proved  that  "the  copper  ores  of  a  good 
part  of  the  Southwest  and  also  of  at  least  a  portion  of  the  Utah  region 
contain  chalcocite,  which  is  not  floatable  by  any  of  the  methods  so  far 
tested."  This  opinion  epitomizes  the  experience  gained  up  to  that 


THE  FLOTATION   PROCESS 


49 


time  in  the  London  laboratory.  Even  in  the  191-i  edition  of  his  book, 
Mr.  Hoover  mentions*  the  presence  of  bornite  and  chalcocite  as  likely 
to  limit  the  successful  operation  of  the  process.  It  is  now  recognized 
that  chalcocite  is  easier  to  float  than  pyrite.  It  is  fair  to  add  that,  at 


T.  J.  HOOVER. 

APPABATDS  TOR  ORE  CONCENTRATION. 
APPLIOATIOH  FILED  MAS.  17, 1909. 


953,746. 


Patented  Apr.  5, 1910. 


€ 


I) 


FIG.  14.   THE  HOOVER  APPARATUS  PATENT. 


*Page  190.    'Concentrating  Ores  by  Flotation.' 


50  THE  FLOTATION   PROCESS 

a  later  date,  one  or  two  important  copper  companies  obtained  an  in- 
creased revenue  thanks  to  the  insistence  of  Minerals  Separation  in 
recommending  the  use  of  their  method.  This  insistence  resulted  in 
valuable  contracts. 

It  is  well  to  warn  the  reader  against  the  inferences  attempted  to  be 
made  from  experiments  in  court,  or  elsewhere,  intended  to  prove  that 
sundry  effects  can  be  obtained  or  cannot  be  obtained  by  following  the 
descriptions  in  various  patents.  As  a  matter  of  fact  the  results  depend 
largely  upon  the  manipulation,  performed  usually  by  an  operator 
who  knows  a  great  deal  that  was  not  known  at  the  time  the  description 
was  written.  Moreover,  the  improvement  in  apparatus  enables-  a  later- 
day  operator  to  apply  recent  knowledge  in  the  course  of  an  experi- 
ment supposedly  based  upon  an  old  method.  By  aid  of  Herodotusf 
and  a  slide  machine  it  is  possible  to  produce  a  performance  that 
might  well  perplex  a  philosopher,  or  a  judge. 

In  Mr.  Hoover's  book  the  average  royalty  levied  by  the  process- 
mongers  is  given  as  1  shilling  or  25  cents  per  ton.  Writing  in  July 
1912,  this  author  stated  that  the  combined  capital  of  all  the  com- 
panies controlling  flotation  processes  was  about  $5,000,000.  As  the 
companies  had  then  been  in  existence  for  7  years,  they  should  have 
treated  38,000,000  tons  in  order  to  return  their  capital  and  10%  per 
annum.  Up  to  that  time  they  had  treated,  he  says,  only  8,000,000 
tons.  Thus  he  drew  a  melancholy  picture.  But  the  adoption  of  the 
process  by  the  big  copper  mining  companies  in  this  country  is  going 
to  make  those  figures  of  four  years  ago  look  small  indeed.  This  year 
20,000,000  tons  will  be  treated  in  the  United  States  alone ;  next  year, 
the  tonnage  may  well  increase  to  30,000,000,  taking  no  count  what- 
ever of  the  operations  in  Australia,  Chile,  British  Columbia,  Korea, 
Mexico,  and  other  parts  of  the  world.  Soon  it  will  be  100,000  tons 
per  day  in  the  United  States  alone.  The  process-mongers  have  a  prize 
worthy  of  a  big  fight  and  the  users  have  an  incentive  to  curb  any 
attempt  to  impose  an  excessive  royalty  accompanied  by  an  embargo 
upon  knowledge.  That  is  where  Minerals  Separation  has  antagonized 
so  many.  They  have  claimed  royalties  where  previously  they  had  re- 
ported that  the  ore  was  unsuitable  to  flotation.  Some  of  the  com- 
panies that  are  now  operating  successfully  .went  first  to  Minerals 
Separation  for  guidance  and  obtained  so  little  assistance  that  they 


fWho  has  told  us  about  the  maidens  dwelling  upon  a  mysterious  island 
on  which  there  was  a  lake  of  pitch.  The  maidens  went  to  this  lake,  dipped 
their  feathers  in  the  pitch,  and  then  proceeded  to  another  lake  where  they 
extracted  gold  from  the  sand  by  trailing  their  pitchy  feathers. 


THE   FLOTATION   PROCESS  51 

had  to  solve  their  own  difficulties  for  themselves.  One  or  two  big 
companies  have  won  reasonable  terms;  for  instance,  it  has  been  dis- 
closed that  the  Anaconda  and  Inspiration  companies  have  guaranteed 
that  if  the  Supreme  Court  reverses  the  Hyde  case,  or  if  they  do  not 
exercise  their  option  to  surrender  their  license  in  case  of  affirmance, 
they  will  treat  25,000,000  tons  of  ore  by  the  Minerals  Separation 
method  by  1923,  and  will  pay  the  agreed  royalty  thereon,  this  royalty 
being  f  cent  per  pound  of  copper,  but  not  less  than  12  cents  per  ton 
of  ore ;  and  meanwhile,  whatever  the  decision  of  the  Supreme  Court, 
they  have  agreed  to  pay  a  royalty  of  $300,000  to  Minerals  Separation 
within  a  year  from  date — nine  months  ago.  Having  regard  to  the  fact 
that  the  extraction  by  flotation,  as  compared  with  ordinary  water 
concentration  has  been  improved  from  63  to  95%,  at  no  greater  cost 
in  plant  or  of  operation,  it  is  obvious  that  the  copper  companies  can 
well  afford  to  pay  such  a  royalty,  if  the  improvement  is  due  to  the 
use  of  patents  owned  by  Minerals  Separation.  That  point  the  Su- 
preme Court  will  decide  at  an  early  date. 

But,  as  I  have  said,  it  is  not  the  amount  of  the  royalty  but  the 
method  of  levying  tax  and  the  attempt  to  place  an  embargo  on  all 
information  concerning  the  technique  of  the  process  that  has  aroused 
opposition.  The  type  of  contract  made  with  licensees  has  caused 
many  operators  to  refuse  to  come  to  terms;  but  the  more  objection- 
able practice  has  been  the  enforcement  of  binding  contracts  on  the 
metallurgists  employed  by  the  licensees,  such  contracts  being  legally 
invalid  and  representing  an  attempt  to  bluff  the  profession.32 

For  the  most  part,  until  quite  recently,  the  information  available 
on  the  flotation  process  has  come  from  patentees,  their  friends,  and 
their  enemies;  a  good  many  of  the  facts  available  have  been  elicited 
in  the  course  of  litigation,  which  has  now  been  in  progress  for  ten 
years;  therefore  a  vast  amount  of  non-science  has  been  mixed  with 
the  little  science  that  has  survived  amid  thoroughly  uncongenial  sur- 
roundings. Anybody  familiar  with  the  bitter  business  feuds  and  per- 
sonal vendettas  generated  during  the  course  of  quarrels  over  patent 
rights  needs  not  to  be  told  that  keen  prejudice,  amounting  in  some 
cases  to  malice,  has  been  injected  into  the  ragged  literature  of  flota- 
tion. The  warping  of  scientific  vision  is  astounding  to  the  detached 
observer.  Much  that  has  got  into  print  and  more  that  has  escaped  a 
permanent  record  has  been  written  with  a  jaundiced  eye  on  the  law- 
courts.  On  top  of  this  the  metallurgy  of  the  subject  has  been  placed 

32'Minerals  Separation  Contracts  with  Metallurgists,'  Mining  and  Scien- 
tific Press,  February  5,  1916.    Also  'A  Professional  Matter/  in  the  same  issue. 


52  THE  FLOTATION   PROCESS 

under  an  embargo  of  secrecy  by  the  owners  of  the  chief  patents,  and 
this  has  been  effective  to  the  extent  of  preventing  the  technical  men 
in  the  employ  of  the  process-mongers  from  contributing  to  current 
knowledge.  Only  recently  has  there  been  any  considerable  contribu- 
tion from  independent  sources  of  information. 

Another  important  element  in  retarding  the  technology  of  the 
process  is  the  ignoring  of  the  fact  that  it  depends  far  more  on  physical 
than  on  chemical  considerations.  To  the  physicist,  not  the  chemist, 
we  must  look  for  guidance.  The  metallurgist  hitherto  has  depended 
upon  chemistry  to  guide  him;  he  must  now  go  back  to  school  and 
acquire  something  more  than  a  smattering  of  physics,  if  he  expects 
to  understand  the  problems  of  the  new  process.  To  most  of  us 
chemistry  comes  more  easily  because  it  has  a  sign  language,  that  of 
the  formula,  to  convey  ideas,  while  physics  depends  upon  the  use  of 
terms,  half  of  which  beg  the  question.  Hence  the  student  must  begin 
by  rejecting  the  use  of  terms  that  he  does  not  understand,  and  when 
he  has  learned  to  understand  them  he  must  take  pains  to  define  them 
whenever  he  undertakes  to  convey  his  ideas  to  others.  By  such  sin- 
cerity of  thought  it  will  be  possible  to  make  real  progress,  and  to 
apply  science  to  industry  with  results  far  transcending  any  hitherto 
achieved  in  this  field  of  human  activity. 


FLOTATION  TESTS  AT  MOUNT  MORGAN  53 

FLOTATION   TESTS   AT   MOUNT   MORGAN 

By  WILLIAM  MOTHERWELL 
(From  the  Mining  and  Scientific  Press  of  June  27,  1914) 

The  Mount  Morgan  gold  mine  in  Queensland,  Australia,  which 
was  discovered  about  30  years  ago,  is  believed  to  be  the  richest 
individual  gold  mine  ever  found,  having  produced  over  $70,000,000 
worth  of  gold  to  date,  besides  copper.  In  its  early  stage,  the  ore, 
which  carried  hundreds  of  ounces  to  the  ton,  was  crushed  with 
stamps  and  amalgamated,  but  the  recovery  was  not  especially  good. 
Subsequently,  and  until  seven  years  ago,  all  the  ore  was  dry-crushed 
in  ball-mills,  roasted,  and  leached  with  chlorine  solution  in  open 
brick  vats  and  the  gold  precipitated  on  charcoal.  At  that  time  the 
copper  content  of  the  ore  was  negligible.  This  is  one  of  the  few 
large  gold  mines  in  the  world  that  never  had  a  cyanide  plant. 

About  eight  years  ago,  a  large  body  of  rather  silicious  cupriferous 
sulphide  ore  was  found  in  the  mine.  Blast-furnaces  were  erected, 
and  the  less  silicious  ore,  which  contained  about  $10  gold,  4% 
copper,  and  45%  silica,  was,  and  still  is,  being  smelted.  The  more 
silicious  or  so-called  'mundic'  ore,  carrying  about  $15  gold  and  1% 
copper,  was  then  dry-crushed,  roasted,  leached  with  sulphuric  acid, 
the  copper  being  precipitated  on  scrap-iron,  subsequently  leached  in 
the  same  vats  with  chlorine  solution,  and  gold  precipitated  as  before 
mentioned.  About  18  months  ago  the  gold  content  of  this  'mundic' 
ore  began  to  decrease,  and  the  copper  content  to  increase.  For  this 
and  other  reasons  it  was  deemed  advisable  to  cease  this  method  of 
treatment,  and  the  last  of  the  chlorination  works  was  shut  down. 

It  now  became  necessary  to  find  a  profitable  method  of  handling 
this  class  of  ore.  As  iron-bearing  flux  has  to  be  brought  a  long 
distance,  and  as  the  ore  carries  about  70%  of  insoluble,  smelting 
would  be  too  expensive.  There  is  believed  to  be  at  least  2,500,000 
tons*  of  this  class  of  ore  in  the  mine,  assaying  roughly  $6  gold  and 
2%  copper.  This  is  in  addition  to  the  so-called  'copper  ore'  which 
is  being  smelted.  It  may  be  explained  that  there  is  no  'carbonate 
zone'  in  this  mine.  All  the  copper  is  in  the  form  of  chalcopyrite. 
The  gold  is  very  fine. 

MINERALS  SEPARATION  EXPERIMENTS 

A  few  years  ago  some  experiments  were  made  by  crushing  in 


*The  long  ton,  2240  lb.,  is  used  throughout  this  article. 


54  THE  FLOTATION   PROCESS 

ball-mills  and  concentrating  on  Wilfley  tables,  but  they  were  not 
successful.  Last  year  it  was  decided  to  make  a  thorough  trial  of 
the  Minerals  Separation  process,  and  a  small  testing  plant  was  erected 
in  the  laboratory.  At  the  same  time  a  full-sized  experimental  unit, 
capable  of  treating  300  to  400  tons  per  24  hours,  was  erected  in 
one  of  the  abandoned  chlorination  plants.  Both  sets  of  experiments 
were  carried  out  by  the  metallurgical  staff  of  the  Company.  After 
they  were  finished,  a  representative  of  the  Australian  branch  of 
Minerals  Separation,  Ltd.,  paid  a  visit  to  the  mine  and  conducted 
a  few  tests,  which  confirmed  the  results  obtained  by  the  mine  staff. 

As  mentioned  in  the  Company's  annual  report,  these  flotation 
experiments  were  successful,  the  extraction  being  higher  and  the 
costs  lower  than  expected.  The  company  is  now  building  the  first 
unit  of  a  plant  to  treat  1000  tons  per  24  hours.  The  ore  will  be 
crushed  by  rock-breakers,  Symons  disc  crushers,  rolls,  and  tube-mills. 
It  will  then  be  concentrated  on  Wilfley  tables,  after  which  it  will 
go  through  a  second  set  of  tube-mills,  thence  to  the  flotation  machines. 
It  is  presumed  that  no  royalty  will  be  payable  on  the  Wilfley 
concentrate.  This  concentrate  will  either  be  briquetted  or  sintered 
in  a  Dwight-Lloyd  machine,  and  smelted  in  blast-furnaces  along  with 
the  'copper  ore'  and  ironstone  and  limestone  fluxes.  The  Company 
has  no  reverberating  furnaces. 

APPLICATION  OF  FLOTATION  TO  GOLD  ORE 

A  flotation  plant  is  being  erected  at  the  Falcon  mine,  Rhodesia, 
to  treat  ore  containing  gold  and  copper.  With  the  exception  of  the 
Mt.  Morgan,  the  Etheridge,  and  the  Great  Fitzroy  mines,  Queensland, 
I  have  not  heard  of  the  flotation  process  being  used  successfully  to 
treat  ore  containing  an  appreciable  amount  of  gold.  The  Elmore 
thick  oil  process  was  installed  at  the  Lake  View  Consols  gold  mine, 
Kalgoorlie,  several  years  ago,  but  was  not  successful,  as  the  ore 
was  not  suitable,  and  unsuccessful  experiments  were  made  by  Minerals 
Separation,  Ltd.,  on  ore  from  the  Lancefield  mine,  Western  Australia, 
which  contains  mispickel.  The  Elmore  vacuum  process  was  installed 
at  the  Cobar  gold  mines,  New  South  Wales,  and  at  the  New  Ravens- 
wood  gold  mines,  Queensland.  Both  these  mines  contain  copper  in 
the  form  of  sulphide,  as  well  as  gold,  but  the  plants  only  ran  a  few 
weeks.  I  was  informed  that  the  plant  at  the  former  mine  (where 
the  ore  contains  about  $8  gold  and  1.5%  copper)  gave  a  fair  recovery 
of  copper,  but  left  too  much  gold  in  the  tailing  or  left  enough 
copper  in  the  tailing  to  prevent  profitable  cyanidation  of  the  gold. 


FLOTATION  TESTS  AT  MOUNT  MORGAN  55 

To  return  to  the  Mt.  Morgan  mine,  the  laboratory  apparatus 
had  a  capacity  of  one  pound  of  ore  at  a  time,  and  the  results  now 
being  obtained  in  the  experimental  mill  approximate  closely  those 
obtained  in  the  laboratory.  The  object  of  concentration  was,  of 
course,  to  obtain  a  concentrate  containing  as  much  gold,  copper, 
and  iron,  and  as  little  silica  as  possible,  commensurate  with  a  good 
extraction  of  the  gold,  because  it  was  found  that  the  less  silica  the 
concentrate  contained  the  poorer  was  the  extraction  of  gold.  It 
costs  13  cents  to  flux  one  unit  of  silica,  and  it  was  necessary  to  steer 
a  middle  course.  Experiments  made  with  Sonstadt  solution  on  ore 
from  one  part  of  the  mine  showed  that  clean  quartz  (after  separation 
by  specific  gravity  from  all  mineral)  contained  not  less  than  $1.50 
gold  per  ton.  In  practice,  of  course,  it  is  impossible  to  float  all 
the  mineral  and  sink  all  the  gangue. 

The  agitator  in  the  laboratory  plant  was  at  first  run  at  1100 
r.p.m.,  but  was  afterward  reduced  to  800.  Tests  were  made  with 
pulps  of  different  proportions,  each  separate  pulp  being  agitated  for 
the  same  length  of  time,  that  is,  6  minutes,  and  it  was  found  that 
there  was  not  much  difference,  in  the  extraction  of  gold  and  copper, 
between  a  pulp  containing  three  parts  solution  to  one  of  ore,  and 
a  pulp  containing  seven  parts  solution  to  one  of  ore.  A  pulp  of 
1  to  1  was  too  thick  and  gave  poor  results.  In  practice,  the  thinner 
the  pulp  the  smaller  the  capacity  of  the  flotation  machine.  Tests 
were  also  made  to  ascertain  the  effect  of  agitating  for  different 
lengths  of  time.  Two  tests  were  made  in  the  laboratory  of  which 
I  have  a  note:  one  for  10  minutes  and  one  for  15  minutes.  The 
ore  contained  $6.50  gold  and  2%  copper;  12%  of  this  sample  would 
remain  on  a  60-mesh  screen.  The  first  one  gave  a  concentrate 
containing  $22.70,  9.4%  copper,  and  18%  insoluble,  with  an  extrac- 
tion of  51%  of  the  gold  and  84.5%  of  copper.  The  second  gave  a 
concentrate  containing  $20.20  gold,  7.8%  copper,  and  27%  insoluble, 
with  an  extraction  of  64.5%  of  gold  and  91.8%  copper.  The  gold 
left  in  the  tailing  was  probably  in  the  gangue,  as  the  extraction  was 
poorer  than  usual.  As  a  rule,  the  longer  agitation  and  separation 
are  continued,  the  more  silicious  the  concentrate  is.  In  practice, 
the  length  of  treatment  is  regulated  by  the  thickness  of  pulp  and 
the  number  of  boxes  in  the  flotation  machine.  Tests  made  to  ascer- 
tain to  what  degree  fine  crushing  was  necessary  showed  emphatically 
that  the  ore  must  all  pass  through  a  screen  of  60  holes  to  the  linear 
inch  if  a  good  extraction  is  to  be  obtained,  and  that  the  finer  it 
was  crushed,  at  any  rate  down  to  120-mesh,  the  better  the  extraction 


56  THE  FLOTATION   PROCESS 

was.  Tests  showed  that  when  using  eucalyptus  oil  there  was  no 
advantage  in  using  an  acid  solution,  but  that,  on  the  other  hand, 
slight  acidity  did  no  harm.  Much  of  the  copper  pyrite  in  the  ore 
readily  floats  on  water  without  any  previous  agitation.  On  treating 
ore  containing  $25  gold  direct  by  agitation  and  flotation,  without 
amalgamating  or  concentrating  on  tables,  it  was  proved  that  fine 
free  gold  can  be  floated  by  using  eucalyptus  oil. 

USE  OP  ESSENTIAL  OILS 

Many  oils  were  tested,  and,  generally  speaking,  it  was  found 
that  only  essential  oils  gave  a  coherent  froth  and  good  extraction, 
other  oils  like  petroleum,  oleic  acid,  and  lubricating  oils  tending 
to  form  granules  which  sank.  The  best  results  were  obtained  from 
eucalyptus,  closely  followed  by  '  Essential  C'  and  Pinus  laurus 
vulgaris.  Oleic  acid,  which  was  used  for  years  at  Broken  Hill  on 
zinc  ore  with  hot  solution,  and  gave  good  results  when  tried  on  this 
ore  with  neutral  and  acid  solutions,  gave  an  enormous  froth  and 
floated  most  of  the  silica.  A  mixture  containing  95%  of  eucalyptus 
and  only  5%  of  oleic  acid  gave  a  concentrate  containing  47%  silica, 
showing  the  power  of  the  oleic  to  float  silica.  Experiments  were 
afterward  made  with  a  mixture  of  oils,  and  one  combination  (known 
as  Mt.  Morgan  mixture)  was  found  to  give  a  better  extraction  of 
both  gold  and  copper  than  any  of  the  individual  oils,  and  at  less 
expense.  When  the  sample  was  all  crushed  to  pass  80  mesh,  an 
extraction  of  80%  of  the  gold  and  90%  of  the  copper  could  be 
obtained  every  time,  with  a  concentrate  containing  about  25% 
insoluble,  which  can  be  reduced  to  10%  by  re-treatment.  Hot  solu- 
tions and  a  solution  containing  1%  of  common  salt  were  found  to 
be  detrimental  to  good  recoveries. 

RECOVERY  BY  FLOTATION 

A  test  on  a  sample,  crushed  to  pass  a  screen  of  120  holes  per 
linear  inch,  containing  $37  gold  and  4.8%  copper,  gave  a  recovery 
by  flotation  alone  of  90%  of  the  gold  and  98.5%  of  the  copper,  but 
left  $8  gold  in  the  tailing.  The  concentrate  carried  44%  insoluble 
matter,  which  could  be  reduced  by  re-treatment.  A  different  oil 
(eucalyptus)  would  have  given  a  poorer  recovery  and  a  cleaner 
concentrate. 

Tests  made  on  ore  containing  $9  gold,  3.5%  copper,  and  45% 
insoluble,  showed  that  after  crushing  to  pass  60  mesh  and  treating 
by  direct  flotation,  an  extraction  of  82%  of  the  gold  and  96%  of 


FLOTATION  TESTS  AT  MOUNT  MORGAN  57 

the  copper  could  be  obtained,  with  a  concentrate  containing  only  21% 
insoluble.  No  doubt  with  finer  crushing  even  better  recoveries  would 
be  had.  These  results  leave  tables  and  vanners  far  behind.  It  was 
found  decidedly  advantageous  to  re-use  the  solutions. 

A  Wilfley  table  was  erected  in  the  mill,  some  tests  made,  and 
the  tailing  treated  by  flotation  in  the  laboratory.  Sometimes  these 
tailing  samples  were  dried  before  flotation,  and  sometimes  they  were 
not.  It  was  invariably  found  that  a  better  extraction  was  obtained 
from  those  which  had  not  been  dried,  as  no  matter  how  carefully 
the  operation  was  conducted,  some  of  the  iron  pyrite  got  sufficiently 
oxidized  to  resist  flotation,  and  it  carried  some  of  the  gold. 

In  some  of  the  tests  the  crushed  ore  was  concentrated  by  panning 
in  the  laboratory,  and  afterward  subjected  to  flotation.  In  this  case 
the  water  in  the  laboratory  was  used,  which  did  not  come  froih  the 
same  source  as  the  water  used  in  the  mill.  It  was  noticed  that  the 
longer  the  sample  was  allowed  to  remain  in  the  water  after  panning, 
the  worse  the  subsequent  flotation  was.  For  example,  where  flotation 
took  place  immediately  after  vanning,  the  residue  assayed  $2.60  gold 
and  0.30%  copper,  but  where  tailing  from  panning  was  allowed  to 
remain  under  water  for  6  hours  before  flotation,  the  residue  assayed 
$3.10  gold  and  0.67%  copper.  An  analysis  of  this  water  was  made, 
and  this  incident  shows  what  might  happen  in  a  mill  where  the  ore 
is  in  contact  with  bad  water  for  some  hours  before  reaching  the 
flotation  machine,  such  as  the  time  it  is  going  through  rolls,  Chilean 
mills,  tube-mills,  and  classifiers,  over  tables  and  through  thickening 
devices,  and  perhaps  through  secondary  tube-mills.  The  water  in 
question  was  neutral,  both  before  and  after  coming  in  contact  with 
the  ore. 

Some  tests  were  made  both  in  mill  and  laboratory  in  which 
air  was  drawn  into  the  agitation  boxes  through  pipes  fixed  vertically 
in  the  corner  with  the  top  open  to  the  air  and  the  bottom  ending 
in  a  bent  pipe  terminating  under  the  impeller  of  the  agitator.  No 
improvement  was,  however,  noticeable. 

Grading  tests  were  conducted  on  crude  ore  and  flotation  products. 
They  showed  that  as  regards  crude  ore,  after  crushing  either  in  mill 
or  laboratory,  the  finest  grade  of  concentrate  or  ore  was  the  richest 
and  the  coarsest  grade  of  tailing  was  richest,  both  in  gold  and  copper. 
The  fact  that  the  finest  grade  of  tailing  was  the  poorest  shows  that 
this  process  will  float  the  finest  sulphides  successfully. 

CRUSHING  PLANT 
In  the  experimental  mill  the  ore  is  crushed  in  rock-breakers  and 


58  THE  FLOTATION   PROCESS 

Krupp  dry-crushing  ball-mills  without  drying.  This  plant  was 
formerly  used  to  crush  oxidized  ore  for  chlorination  and,  being  on 
the  spot,  it  was  naturally  utilized  in  preference  to  buying  new 
machinery.  The  crushed  ore  drops  into  a  bin  at  the  bottom  of 
which  are  two  Challenge  feeders.  These  deliver  the  ore  into  a 
launder  where  it  is  met  by  a  stream  of  water  which  carries  it  direct 
to  a  six-compartment  Minerals  Separation  machine.  Each  spindle 
is  driven  by  a  half-crossed  belt,  thus  eliminating  the  noise  and  grease 
incidental  to  the  old  Broken  Hill  method  of  gearing.  The  machine 
is  of  the  Hoover  single-level  type,  by  which  one  man  can  attend  to 
all  the  flotation  boxes.  The  concentrate  was  collected  at  first  in 
circular  wooden  vats  with  filter-bottoms  of  cocoa  matting,  and  later 
in  shallow  rectangular  concrete  tanks  which  formed  part  of  the  old 
chlorination  works.  The  whole  plant  is  extremely  simple  and 
requires  very  few  men  to  run  it.  It  has  not  been  found  practicable 
to  use  a  screen  finer  than  35  mesh  on  the  ball-mills.  It  is  found 
that  the  gold,  copper,  and  iron  contents  are  greater  in  the  concen- 
trate overflowing  from  No.  1  box  and  that  they  gradually  decrease 
until  No.  6  is  reached,  while  the  silica  content  increases  from  10% 
in  the  concentrate  from  No.  1  box  to  about  50%  in  that  from  No.  6. 
About  56  hp.  is  required  to  drive  the  agitators  at  350  revolutions 
per  minute. 

As  it  is  intended  to  use  Wilfley  tables  in  the  new  mill  to  assist 
in  recovering  the  iron  pyrite  in  the  ore  for  fluxing  and  other 
purposes,  two  of  these  machines  were  placed  in  the  experimental 
mill  and  some  tests  made  to  find  out  what  results  may  be  expected 
of  them.  Taking  an  average  of  several  tests  on  ore  from  different 
parts  of  the  mine,  the  grading  of  the  'table  feed'  was  as  follows: 
10%  remained  on  60  mesh,  and  19%  passed  through  60  but  remained 
on  120  mesh.  It  contained  $4.50  gold,  1.8%  copper,  9%  iron,  and 
76%  insoluble.  The  concentrate  assayed  $17  gold,  2.9%  copper,  34% 
iron,  and  18%  insoluble;  the  recoveries  were  33%  of  the  gold,  13%  of 
the  copper,  and  38%  of  the  iron.  No  doubt,  had  the  pulp  been 
classified  and  the  fine  material  passed  over  slime  tables  or  vanners, 
better  results  would  have  been  obtained,  but  the  Company  does  not 
intend  to  use  mechanical  concentrators  for  the  slime,  preferring  to 
rely  on  the  flotation  process,  so  it  was  not  worth  while  experimenting 
with  them. 

During  the  flotation  experiments  with  eucalyptus  oils  some  tailing 
was  produced  which  contained  a  fair  amount  of  gold,  and  attempts 
were  made  to  recover  some  of  this  by  amalgamating  and  cyaniding. 


FLOTATION  TESTS  AT  MOUNT  MORGAN  59 

It  was  found  that  no  extraction  by  amalgamation  was  possible,  nor 
was  any  extraction  by  cyaniding  possible  without  either  roasting 
or  finer  grinding.  On  unroasted  tailing  assaying  $3  gold  and  0.44% 
copper,  after  crushing  to  pass  120  mesh,  separating  the  slime,  and 
leaching  the  sand  for  9  days,  an  extraction  of  only  60c.  per  ton 
was  obtained  with  a  consumption  of  3.6  Ib.  of  cyanide  per  ton. 
On  a  different  tailing  crushed  to  pass  80  mesh,  which  after  slime 
was  separated  assayed  $2.90  gold  and  0.30%  copper,  an  extraction 
of  $1  was  obtained  in  5  days  with  a  consumption  of  2  Ib.  of  cyanide. 
Samples  of  slime  were  treated  by  agitation  and  washed  by 
decantation,  and  gave  slightly  better  extractions,  but  the  consump- 
tion of  cyanide  went  up  to  6  or  7  Ib.  The  strength  of  solution 
used  in  these  tests  was  0.10%  KCN.  It  should  perhaps  be  noted 
that  all  samples  of  flotation  tailing  had  been  dried  before  being 
tested  by  cyanidation. 

EFFECT  OF  ROASTING 

Two  samples  of  sand  from  tailing  were  roasted  and  treated  by 
percolation.  The  value  was  $3.  The  roasting  reduced  the  sulphur 
to  0.5%.  Although  the  copper  and  iron  were  oxidized  by  roasting, 
the  consumption  of  KCN  was  less  than  in  treating  the  unroasted 
tailing,  which  was  contrary  to  expectation.  With  three  days  treat- 
ment, the  residue  was  reduced  to  $1  per  ton,  and  about  one-third 
pound  of  copper  was  dissolved  from  each  ton  of  tailing  by  the 
cyanide.  The  consumption  of  cyanide  was  1.4  Ib.  per  ton,  so  that 
the  extraction  was  higher  and  the  loss  of  cyanide  less  than  in 
treating  unroasted  tailing.  Speaking  from  memory,  I  think  that 
attempts  to  regenerate  the  cyanide  in  solution  by  means  of  sulphuric 
acid  and  lime  were  not  very  successful.  The  solution  contained  0.05 
gram  copper  per  litre. 

These  cyaniding  tests  were  merely  done  for  information,  as  it 
is  not  expected  that  the  tailing  from  the  new  mill  will  be  profitable 
for  cyaniding.  The  subject  of  extracting  gold  from  flotation  tailing 
arose  a  few  years  ago  at  the  Cobar  gold  mines,  as  already  mentioned, 
but  in  that  case  the  difficulty  was  overcome  by  selling  the  mine, 
which  contained  highly  silicious  ore,  to  a  company  which  owned  a 
smelter,  and  had,  or  thought  it  had,  plenty  of  basic  ore  for  flux. 
Unfortunately,  the  amount  had  been  overestimated  and  the  problem 
is  still  unsolved — but  that  is  another  story. 


60  THE  FLOTATION   PROCESS 

OILS   USED   IN   THE    FLOTATION   PROCESS 

By  AN  OCCASIONAL  CONTRIBUTOR 
(From  the  Mining  and  Scientific  Press  of  May  1,  1915) 

INTRODUCTORY. — The  work  of  the  past  two  years  at  many  mills  in 
the  United  States,  Mexico,  and  South  America,  has  done  much  to 
prove  the  suitability  of  flotation  processes  to  the  recovery  of  the  sul- 
phide ores  of  copper,  and  to  indicate  the  best  reagents.  In  a  general 
way,  it  may  be  said  that  oils  of  mineral  origin,  such  as  coal-tar  and 
fuel-oil,  give  better  results  on  copper  ores,  while  oils  of  vegetal  origin, 
such  as  the  terpenes,  pinenes,  wood-tars,  etc.,  are  better  adapted  for 
the  treatment  of  zinc  and  lead  ores. 

COAL-TAR  PRODUCTS. — Among  these  cresylic  and  carbolic  acids  are 
the  best  known  reagents.  Commercial  cresylic  acid  is  an  oily  refrac- 
tive liquid,  generally  with  a  red  or  yellow  tinge,  has  a  specific  gravity 
of  about  1.044,  and  consists  of  approximately  40%  metacresylic,  35% 
orthocresylic,  and  25%  paracresylic  acids,  the  properties  of  these 
three  isomers  being,  according  to  Lunge  and  Keane  r1 

Solubility  in  100 

parts  water,  ordi- 

Acid.  B.P.  nary  temperature. 

Orthocresylic 191°  2.50  vol. 

Metacresylic    203°  0.53     " 

Paracresylic 202°  1.80     " 

This  acid  is  much  less  soluble  in  water  than  its  homologue,  carbolic 
acid,  and  is  still  more  easily  broken  down  by  sulphuric,  which  probably 
accounts  for  the  statement  that  sulphuric  acid  may  not  be  used  along 
with  either  of  these  weaker  acids.  My  own  experiments  .give  conflict- 
ing results,  and  I  cannot  speak  with  confidence  on  this  point. 

I  have  found  a  marked  difference  in  the  behavior  of  different 
brands  of  cresylic  acid,  and  I  suggest  that,  in  conjunction  with  tests 
run,  the  different  brands  be  analyzed  to  see  what  bearing  the  differ- 
ing amount  of  the  three  constituents  has  on  the  action  of  the  various 
acids,  I  had  very  poor  success  in  treating  a  certain  chalcocite  ore  with 
a  dark  colored  cresylic  acid,  and  on  changing  over  to  a  light  colored 
brand,  I  had  immediately  surprisingly  good  results. 

Lunge  and  Keane  give  a  method  (Rascheg's)  for  the  estimation  of 
the  three  isomers  of  cresylic  acid.  For  the  benefit  of  those  who  may 
not  have  access  to  this  book,  I  give  it  in  full : 


I'Technical  Methods  of  Chemical  Analysis,'  1911. 


OILS  USED  IN  THE  FLOTATION  PROCESS  61 

On  treating  m-cresol  with  excess  of  HN03,  at  100°  it  is  quantita- 
tively converted  into  trinitrocresol,  while  its  isomers  are  completely 
oxidized  to  oxalic  acid.'  The  following  directions,  which  must  be 
most  carefully  observed,  give  reliable  results:  Exactly  10  grammes 
of  the  cresol  mixture  are  weighed  into  a  small  conical  flask  mixed  with 
15  c.c.  ordinary  H2S04  (1.84),  then  treated  for  1  hour  in  a  steam- 
oven,  and  the  contents  poured  into  a  wide-necked  flask  of  1  litre 
capacity.  The  flask  is  cooled  under  the  tap,  shaking  it  round  mean- 
while in  such  a  manner  that  the  sulphonic  acid,  which  is  a  mobile 
liquid  while  hot,  settles  as  a  thick  syrup  on  the  sides  of  the  flask  during 
cooling.  90  c.c.  of  HN03  (1.38)  are  then  first  poured  into  the  small 
flask  in  which  the  sulphonation  was  conducted,  in  order  to  remove 
any  sulphonic  acid  adhering  to  its  sides,  rinsed  well  round,  and  then 
poured,  all  at  once,  into  the  larger  flask.  The  contents  of  the  latter 
are  well  shaken  immediately,  so  that  all  the  sulphonic  acid  is  dis- 
solved, which  takes  about  20  seconds.  The  flask  is  then  placed  in  a 
draught -cupboard.  After  one  minute  a  violent  reaction  occurs,  red 
fumes  are  evolved,  and  the  liquid  boils ;  then  it  suddenly  becomes 
turbid;  oily  drops  of  trinitrocresol  form  and  collect  on  the  bottom 
of  the  flask;  and  after  five  minutes  the  reaction  is  apparently  ended. 
The  whole  is  allowed  to  stand  for  at  least  another  five  minutes,  then 
poured  into  a  dish  containing  40  c.c.  water  and  the  flask  rinsed  out 
with  a  further  40  c.c.  water  into  the  same  dish.  On  mixing  with  water 
the  trinitro-m-cresol  solidifies  with  liberation  of  nitrous  fumes  to  a 
crystalline  magma,  It  is  allowed  to  stand  for  at  least  two  hours  while 
the  liquid  cools;  then  it  is  crushed  with  a  pestle,  and  filtered  on  the 
pump  through  a  filter  that  has  been  tared  against  another  one.  The 
crystals  of  trinitrocresol  are  washed  with  10  c.c.  H20,  dried  at  95  to 
100°  and  weighed.  If  these  instructions  are  carefully  followed,  1.74 
gm.  of  trinitro-m-cresol  are  obtained  for  each  gramme  of  metacresol 
present  in  the  mixture  whatever  the  composition  of  the  latter.  The 
presence  of  even  10%  phenol  does  not  diminish  the  accuracy,  as  the 
picric  acid  that  is  formed  remains  in  solution,  but  the  method  must 
not  be  applied  to  mixtures  containing  large  amounts  of  phenol.  This, 
however,  does  not  often  occur  in  practice.  'In  such  samples  the 
presence  of  phenol  is  detected  by  the  B.P.  and  also  by  the  fact  that 
the  nitro  compound  does  not  remain  solid  in  the  steam-oven  at  95 
to  100°,  but  melts,  or,  at  any  rate,  forms  a  soft  paste.  But  a  cresol 
that  distils  for  the  most  part  between  190  and  200°  and,  therefore, 
contains  scarcely  any  phenol,  always  yields  a  pale  yellow  crystalline 
mass,  the  weight  of  which  divided  by  1.74  gives  the  weight  to  within 


62  THE  FLOTATION   PROCESS 

1%  of  the  m-cresol  in  the  mixture.  It  may  be  well  to  repeat  that  not 
less  than  90  c.c.  of  HN03  is  used,  and  poured  all  at  once  into  the 
flask  as  quickly  as  possible,  a  flask  having  a  very  wide  neck  being  used. 
To  determine  all  three  isoiners  Rascheg  separates  the  o-cresol  com- 
pletely by  repeated  fractional  distillation;  the  distillates  being  com- 
posed roughly  of  60%  m-  and  40%  p-cresol  in  which  the  m-cresol  is 
determined  as  above.  This  operation,  however,  is  entirely  beyond  the 
skill  and  resource  of  the  average  chemist.  It  is  rendered  unnecessary 
from  the  fact  that  the  three  acids  mentioned  bear  a  fairly  constant 
ratio,  as  before  stated,  in  any  commercial  cresylic  acid;  from  the 
percentage  of  meta-cresylic  acid  formed,  the  others  may  be  calcu- 
lated. These  three  acids  can  be  obtained  in  a  pure  state.  I  suggest  a 
trial  of  them  on  a  small  scale,  and  I  venture  the  opinion  here  that 
the  ortho-cresylic  acid  is  the  one  that  does  the  work. 

Cresylic  acid  should  be  handled  carefully,  as  it  gives  rise  to  painful 
skin-wounds,  and  may  easily  splash  into  the  operator's  eyes.  It  is 
well  to  keep  a  bottle  of  olive-oil  handy  as  a  remedy. 

COAL-TAR  CRESOLS. — Cresylic  acid  is  an  expensive  reagent,  costing 
at  least  $1.25  per  gallon  delivered  at  Western  American  mills  in 
peace-time.  It  comes  principally  from  Germany  and  England.  A 
search  for  a  cheaper  substitute  has  shown  that  crude  coal-tar  creosote, 
which  is  a  by-product  of  gas-works,  blast-furnaces,  and  gas-producers, 
is  promising.  Samples  from  different  sources  vary  greatly  in  liquidity 
and  chemical  composition  (proportion  of  phenols  and  cresols  present)  ; 
they  well  merit  investigation.  Being  generally  viscous  they  emulsify 
imperfectly,  especially  in  the  cold,  and  while  some  solvent  like  pine- 
oil  or  cresylic  acid  can  be  employed,  such  solvents  are  expensive  and 
tend  to  mask  the  effect  of  the  original  reagent.  It  is  probable  that 
the  employment  of  the  more  liquid  blast-furnace  creosotes,  with 
preliminary  heating,  would  be  attended  with  good  results. 

Carbolic  acid  (phenol)  is  a  homologue  of  cresylic  acid.  It  is 
difficult  to  distinguish  between  them,  the  smell  and  color  being  so 
much  alike.  Carbolic  acid  has  a  solubility  varying  from  4.83%  at 
11°  to  11.83%  at  77°  in  100  parts  of  water.  It  is  easily  broken  down 
by  sulphuric  acid,  yielding  oxalic  acid.  It  appears  to  be  much  less 
selective  than  cresylic  acid  in  its  action  on  metallic  sulphides,  and  a 
slight  excess  brings  over  a  concentrate  high  in  insoluble  matter. 

FUEL-OILS.— My  investigations  cover  Mexican,  Texan,  and  Cali- 
fornian  crude  oils.  From  the  known  difference  in  composition,  it  is 
not  surprising  that  on  any  particular  ore  the  results  are  widely  differ- 
ent. The  metallurgist  should  have  samples  of  all  three  on  hand  when 


OILS  USED  IN  THE  FLOTATION  PROCESS  63 

running  tests.  Fuel-oils  are  not  highly  selective  like  cresylic  acid, 
pine  oils,  etc.,  but  are  strongly  emulsive;  they  serve  the  purpose  of 
giving  body  and  mineral-carrying  power  to  the  relatively  weak  but 
more  selective  froths;  they  are  cheap,  quickly  obtainable,  and,  when 
used  in  moderation,  bring  over  little  gangue.  It  is  well  to  increase 
their  fluidity  by  steam- jacketting  the  container  from  which  they  are 
fed  to  mixing-compartments. 

Gas  Oil  (stove-oil). — This  is  one  of  the  distillation  products  of 
crude  oil.  It  is  a  strong  emulsifying  agent,  which  is,  at  times,  most 
useful.  It  is  worth  a  trial  in  running  tests.  It  must  be  used  in  very 
small  quantities. 

Crude  Wood  Turpentine. — This  is  not  the  ordinary  spirits  of  tur- 
pentine. It  is  a  dark  reddish-brown  liquid  with  a  pungent  smell. 
On  gravity-flow  machines  I  have  found  it  of  little  use,  as  its  action 
in  slight  excess  is  to  bring  over  gangue  freely.  As  an  emulsifier,  I 
much  prefer  fuel-oil  or  tar-oil.  On  machines  through  which  the  flow 
of  pulp  is  maintained  by  mechanical  means,  it  has  been  found  a  valu- 
able reagent  for  the  purpose  of  controlling  the  levels  of  pulp,  through 
its  physical  action  on  froths,  but  this  result  is  achieved  at  the  ex- 
pense of  impure  concentrate,  unless  the  agent  is  used  in  the  strictest 
moderation. 

PINE-OILS,  WOOD-TAR  OILS,  FIR-OILS,  WOOD- CREOSOTES,  ETC. — The 
destructive  distillation  of  soft  woods  yields  a  large  number  of  pro- 
ducts, and  possible  reagents.  I  have  found  the  oils  derived  from 
pine  and  fir  to  be  more  selective  on  chalcopyrite  than  on  chalcocite 
ores.  Wood-tars  and  tar-oils  are  excellent  emulsifiers,  but  it  appears 
that  the  series  in  general  gives  better  results  on  zinc  and  lead  than 
on  copper  sulphides.  I  have  found  pine-oil  used  in  conjunction  with 
crude  sulphuric  acid  to  give  excellent  recoveries  on  weathered  chalco- 
pyrite ores  where  cresylic  acid  had  been  a  complete  failure.  There 
may  be  some  significance  in  the  fact  that  the  action  of  sulphuric 
acid  on  terpenes  (pine-oils)  and  phellandrenes  (crude  eucalyptus- 
oils)  is  to  give  in  both  cases  dipentenes  and  terpinenes.2  I  mention 
this,  as  eucalyptus-oils,  which  are  prohibitive  in  cost  in  America, 
are,  I  understand,  universally  used  in  conjunction  with  sulphuric  acid 
on  zinc  and  lead  ores  in  Australia. 

APPLICABILITY  OF  THE  PROCESS. — T.  J.  Hoover  in  the  latest  edition 
of  his  book  on  flotation3  repeats  the  statement  made  in  the  first 
edition,  that  there  is  a  doubt  if  chalcocite  can  be  recovered  success- 


2'Thorpe's  Dictionary  of  Applied  Chemistry,'  1913. 
s'Concentrating  Ores  by  Flotation/  1912. 


64:  THE   FLOTATION   PROCESS 

fully  by  flotation.  This  surely  is  an  oversight;  110  one  is  more  cog- 
nizant than  Mr.  Hoover  of  the  recent  work  done  in  flotation,  and  I  have 
only  here  to  refer  to  the  very  high  recoveries  that  have  been  made 
on  a  working  scale  on  chalcocite  ores,  in  Arizona,  at  several  large 
mills. 

Cuprite  is  considered  a  difficult  mineral  to  recover  by  flotation. 
In  the  case  of  one  ore  that  has  come  under  my  notice,  in  which  the 
cuprite  occurred  as  a  subsidiary  mineral,  the  saving  amounted  to  a 
small  percentage  only,  certainly  not  as  much  as  an  efficient  slime- 
table  would  have  recovered.  On  the  silicate  and  carbonate  ores  there 
is  probably  no  appreciable  recovery. 

MECHANICAL  SIDE  OF  THE  PROCESS. — In  my  opinion,  the  develop- 
ment of  what  may  be  termed  pneumatic-flotation  processes  by  Callow, 
Flynn,  Towne,  and  others,  constitutes  the  most  distinct  advance  of 
recent  years.  They  consist  of  a  directly  and  cheaply  applied  supply 
of  air-bubbles  in  a  finely  divided  state,  to  assist  in  bringing  to  the 
surface  of  the  pulp  the  already  prepared  sulphides.  The  agitation 
is  cheaply  and  easily  performed,  and  is  quite  subsidiary  to  the  action 
of  aeration  discussed  above.  I  have  found  a  shallow  trough-agitator, 
with  beaters  only  partly  submerged,  quite  sufficient.  The  introduction 
of  a  jet  of  live  steam  into  the  mixing  compartment  is  an  advantage. 
The  pulp  may  flow  through  the  mixing  and  aeration  compartments 
by  gravity  at  the  expense  of  a  trifling  loss  of  head-room.  This  loss  is 
more  than  compensated  by  decreased  power  and  labor  costs,  and 
simplicity  of  working.  Finely  divided  air-bubbles  can  be  directly 
and  perfectly  applied  through  many  forms  of  porous  media  such  as 
canvas,  corundum  stones,  silica-tiles,  sandstone  slabs,  etc.  The  mineral 
particles  are  seized  upon  and  at  once  removed  as  concentrate,  without 
having  to  be  repeatedly  subjected  to  a  sort  of  'fractional  distillation' 
as  in  the  older  systems.  It  is,  in  a  way,  the  converse  of  Elmore's 
vacuum  process,  and  has  the  merit  of  being  positive  in  action  and 
under  perfect  control.  Remarkable  results  have  been  shown  in  the 
economy  of  reagents,  power,  and  labor;  also  in  the  ease  with  which 
such  machines  can  be  started  after  any  of  these  sudden  stops  in- 
cidental to  milling  operations. 


FLOTATION  OF  COPPER  ORES  65 

FLOTATION   OF   COPPER   ORES 

^ 

(Prom  the  Mining  and  Scientific  Press  of  May  29,  1915) 

The  Editor: 

Sir — The  mention  of  my  name  in  your  recent  article  on  this  subject 
tempts  me  to  offer  a  few  remarks  that  may  be  of  general  interest. 

Pneumatic  flotation  is  already  fully  established  in  a  number  of 
places  and  the  results  in  comparison  with  the  other  and  older 
schemes  fully  justify  the  opinion  of  your  correspondent  that  it  con- 
stitutes the  most  distinct  advance  in  flotation  in  recent  years. 

The  first  pneumatic-flotation  plant  in  this  country  was  erected  by 
me  in  February  1914  for  the  National  Copper  Company  at  Mullan, 
Idaho,  a  description  of  which  has  already  been  published.  The  re- 
sults were  fully  up  to  expectations  from  the  very  start.  This  plant 
consists  of  8  rougher  and  2  cleaner  cells  and  treated  500  tons  per  24 
hours.  A  30-hp.  motor  furnished  power  for  all  the  air  necessary  for 
both  mixing  and  separating,  and  the  oil  consumption  averaged  as  low 
as  0.13  Ib.  of  refined  pine-oil  per  ton  of  ore.  It  was  an  ideal  floating 
ore.  Since  then  the  Callow  scheme  has  been  adopted  by  nearly  all 
the  other  mills  in  the  Coeur  d'Alene  for  the  treatment  of  their  lead- 
zinc  fine  sand  and  slime-feed,  and  has  been  a  means  of  simplifying 
their  plants  and  adding  greatly  to  their  recoveries. 

The  other  plants  that  I  have  since  erected  have  followed  the  same 
general  lines  as  were  laid  down  at  the  National,  namely,  air  or 
tube-mill  mixing  and  emulsifying  of  the  "-feed  followed  by  the 
separatory  cells  run  in  parallel.  Recent  results  at  the  Inspiration 
mine  would  indicate  some  advantage  (on  that  ore,  at  least)  in  running 
the  cells  in  series  of  two  instead  of  parallel,  and  without  any  sacrifice 
in  capacity  for  a  certain  set  number  of  cells.  On  an  ore  carrying  a 
large  percentage  of  mineral  there  is  not  much  doubt  that  the  series 
plan  will  give  the  best  results  and  possibly  dispense  with  the  necessity 
for  cleaning  the  concentrate. 

The  various  elements  that  compose  the  scheme  in  general  are 
illustrated  in  the  accompanying  diagram.  The  preparation  of  the 
pulp  by  any  form  of  violent  or  propeller  agitation  is  not  necessary 
for  good  results  with  the  penumatic  process.  Where  the  oil  can  be 
introduced  into  the  tube-mill  no  further  refinement  in  mixing  is 
necessary.  This,  of  course,  cannot  always  be  done  and  in  such 
cases  air-mixing  with  the  Pachuca  becomes  necessary. 

A  standard  separatory  cell  has  a  capacity  that  will  vary  from 


66  THE  FLOTATION   PROCESS 

35  to  75  tons  of  feed  per  24  hours  when  run  in  parallel,  depending 
of  course  upon  the  characteristics  of  the  feed.  Two  cells  in  parallel 
will  have  about  the  same  capacity  as  two  cells  in  series,  but  a  slightly 
lower  tailing  may  be  expected  with  the  series  treatment. 

The  porous  medium  in  the  bottom  of  the  cell  is  a  loosely  woven 
canvas-twill  four  layers  thick,  secured  to  the  upper  surface  of  a 
perforated  plate  with  bifurcated  rivets  and  washers.  This  is  the 
present  standard  construction  and  has  been  adopted  after  a  great 
many  disappointing  experiments  with  other  materials.  It  is  good 
for  a  three  or  four  months'  continuous  campaign,  and  becomes 
inoperative  only  through  the  filling  up  of  the  pores  by  dust  that  has 
been  introduced  by  way  of  the  blower.  Four  or  five  pounds  of 
air-pressure  is  ample  in  all  cases  to  give  the  proper  aeration,  the 
quantity  of  air  varying  from  6  to  10  cu.  ft.  per  square  foot  of  blanket- 
surface.  "When  the  cell  is  properly  adjusted  and  doing  its  best  work 
there  should  be  no  violent  agitation  with  the  cell,  but  only  such 
agitation  as  is  incident  to  proper  aeration.  Any  violent  agitation 
producing  a  surging  of  the  liquid  contents  has  proved  detrimental 
to  good  results. 

A  slope  of  3  in.  per  foot  on  the  bottom  has  been  found  sufficient 
to  treat  all  ordinary  ores  after  crushing  through  30  or  40-mesh. 
Treating  coarser  material  or  ores  that  contain  a  large  percentage  of 
heavy  gangue  (such  as  in  the  Coeur  d'Alene),  it  has  been  found 
advantageous  to  increase  this  to  as  much  as  4J  in.  per  foot  to  prevent 
the  blanketing  of  the  porous  medium  by  coarse  sand  collecting  on 
the  bottom. 

The  air  from  the  separatory  cells  has  so  far  been  furnished  from 
positive  blowers,  but  turbine-blowers  would  be  preferable  where 
the  size  of  the  installation  justifies  their  adoption.  An  air-pressure 
of  15  Ib.  is  ample  for  the  Pachuca  mixer  and  25  cu.  ft.  of  free 
air  per  minute  is  sufficient  volume  for  mixing  250  tons  of  minus 
48-mesh  pulp,  and  of  course  should  be  furnished  from  a  low-pressure 
compressor. 

The  density  of  the  pulp  may  vary  from  2J  :  1  on  a  sandy  feed 
up  to  7  : 1  on  a  strictly  slime-feed.  The  particular  density  is  not 
a  matter  of  so  much  importance  as  that  the  supply  of  pulp  shall 
be  uniform  as  to  its  density,  since  each  variation  in  the  density 
requires  a  readjustment  of  the  oil-supply,  the  quantity  of  oil  required 
increasing  in  proportion  to  the  increased  volume"  of  the  pulp 
independent  of  its  solid  content. 

The  advantages  of  the  pneumatic  scheme  are  greater  recoveries, 


FLOTATION  OF  COPPER  ORES 


67 


0.38 

0.37 

0.30 

0.29 

0.13 

0.43 

0.44 

0.29 

0.24 

0.13 

0.44 

0.50 

0.30 

0.25 

0.16 

0.54 

0.44 

0.34 

0.26 

0.22 

0.58 

0.42 

0.56 

0.43 

0.33 

68  THE   FLOTATION   PROCESS 

less  oil,  greater  simplicity,  and  less  skill  required  to  operate.     The 
difference  in  wear  and  tear  is  obvious. 

Proof  of  the  increased  recoveries  is  shown  in  Table  I,  which 
represents  a  30-day  competition.  It  is  noticeable  that  this  increase 
in  recovery  lies  principally  in  the  finer  and  slime  portions  of  the 

feed. 

TABLE  I 

ANALYSIS   OF   TAILING THIRTY-DAY   PERIOD 

Total  copper.  Copper  oxide 

Flotation  tailing.          Table  tailing,     in  combined 
Mesh.  Weight.        A.P.  P.P.  A.P.  P.P.        tailings. 

-f     65  7.0 

-f  100  15.0 

+  150  : .  12.0 

+  200  9.8 

—  200  56.2 

Average,  all  sizes.  100.0  ...  ...  0.44  0.35 

TABLE  II 

ANALYSIS    OF   CONCENTRATES 

For  the  same  period 

Cu,  Insol.,  Fe,  S, 

Agitating  process  32.34  26.50  15.01  22.79 

Pneumatic  process  31.24  23.70  16.79  23.84 

The  resulting  concentrates  from  the  same  competition  are  shown 
in  Table  II,  which  indicates  that  the  slightly  lower  grade  of  copper 
is  more  than  offset  by  the  lower  insoluble  and  higher  iron  contents. 

The  proof  of  lower  power-consumption  is  that  the  10  cells  of  the 
National  Copper  Co.  were  run  with  a  30-hp.  motor  and  treated  500 
tons  per  day;  the  same  tonnage  treated  by  a  propeller  machine 
would  have  taken  close  on  to  100  hp.  This  figure  has  also  been 
confirmed  at  other  places.  The  power  required  will  vary  from 
2  to  3  kw.-hours  per  ton. 

The  froth  produced  from  the  penumatic  process  is  much  more 
ephemeral  than  that  produced  by  propeller-agitation  machines,  a 
self-evident  advantage  when  it  comes  to  collecting  and  handling  the 
resulting  concentrates. 

Regarding  oils,  the  remarks  of  your  contributor  with  regard 
to  cresylic  acid  and  the  methods  of  analysis  given  are  extremely 
interesting  and  valuable.  So  far  as  my  own  experience  goes,  I  have 


FLOTATION  OF  COPPER  ORES  69 

not  found  cresylic  acid  indispensable;  at  the  present  time  and  price 
it  is  out  of  the  question  as  a  flotation  agent ;  it  would  seem,  moreover, 
that  the  same  results  can  be  obtained  by  the  use  of  less  refined  and 
expensive  reagents.  In  the  Coeur  d'Alene  on  the  zinc-lead  ores, 
wood  creosote  seems  to  give  the  best  results.  The  Inspiration  uses  a 
mixture  of  80%  El  Paso  coal-tar  and  20%  creosote.  At  one  time 
we  used  a  2^. to  5%  addition  of  pine-oil,  but  this  has  since  been 
found  unnecessary.  A  mixture  of  20%  pine-oil,  20%  cresol,  and 
60%  carbolic  was  tried  experimentally  at  the  Miami  mine,  but  just 
as  good  results  were  obtained  by  substituting  Salt  Lake  creosote 
for  the  cresol  and  carbolic.  These  are  both  chalcocite  ores  with 
some  pyrite;  the  chalcocite  is  easier  to  float  than  the  pyrite.  The 
pulp  is  neutral.  The  recoveries  will  approximate  95%  of  the 
sulphide-copper  contents. 

I  have  tried  a  great  many  of  the  wood-oils,  both  the  steam-distilled 
refined  products  and  also  the  destructively  distilled  crude  tars  and 
creosotes,  but  have  generally  come  back  to  the  coal-tar  mixtures. 
The  pine-tar  products  are  excellent  frothers  but  the  coal-tar  products 
seem  to  act  as  collectors,  and  a  combination  of  the  two  is  often  neces- 
sary. Acid  sludge  has  been  used  with  good  success  on  Butte  copper 
ores,  but  the  disadvantages  of  this  are  that  it  requires  heat  and  also 
additional  quantities  of  acid  to  get  the  best  results.  This  means 
working  with  an  acid  pulp  and  prevents  the  introduction  of  the 
oil  into  the  crushing  plant  because  of  the  destructive  effect  of  the 
acid  on  anything  but  a  silex-lined  mill.  Some  ores  work  best  in  an 
alkaline  pulp  and  others  in  a  neutral  one.  -My  own  opinion  is  that 
in  most  cases  the  same  results  can  be  obtained  in  alkaline  or  neutral 
pulp  as  can  be  obtained  in  an  acid  one  and  the  advantage  of  an 
alkaline  or  neutral  pulp  is  self-evident. 

In  one  plant  we  had  an  interesting  experience  of  this  kind.  The 
water-supply  was  limited  and  all  the  milling-water  was  returned 
back  to  the  mill.  The  flotation  results  gradually  deteriorated  as 
the  mill- water  accumulated  acid;  the  more  acid  it  got,  the  poorer 
the  results.  Lime  was  then  added  in  the  tube-mill  and  the  pulp 
made  alkaline ;  this  produced  a  tremendous  increase  in  the  volume 
of  froth  made,  but  without  any  definite  improvement  in  the  tailing. 
By  reducing  the  lime  and  allowing  the  pulp  to  work  back  to  the 
neutral  point  the  results  again  became  normal;  and  it  is  at  the 
neutral  point  that  we  now  do  our  best  work. 

There  is  a  great  deal  of  work  yet  to  be  done  with  oils,  especially 
in  compounding,  modifying,  and  in  making  them  miscible  without 


70  THE   FLOTATION   PROCESS 

heat.  The  right  combination  of  oil  is  everything;  the  quantity  per 
ton  has  less  influence  on  the  results  than  the  right  mixture.  The 
effect  with  too  much  oil  is  mechanical  rather  than  metallurgical; 
too  much  oil  produces  so  much  froth  that  it  overflows  everything 
and  cannot  be  handled  in  the  plant.  Some  experiments  made  in  this 
direction  gave  the  following  results: 

Grade  of  Extrac- 

Oil  per  ton,  concentrate,          tion, 

lb.  %  % 

2     15.55  90.08 

30    9.82  95.91 

100    7.95  93.46 

But  this  is  a  large  subject  and  altogether  beyond  the  scope  of 
these  random  remarks. 

J.  M.  CALLOW. 
Salt  Lake  City,  April  23. 


PREFERENTIAL   FLOTATION  71 

PREFERENTIAL   FLOTATION 

By  0.  C.  RALSTON 
(From  the  Mining  and  Scientfic  Press  of  June  26,  1915) 

INTRODUCTION.  'Preferential'  notation  is  a  specialized  applica- 
tion of  the  flotative  principle  in  the  separation  of  minerals  from  their 
ores.  It  gained  its  first  wide  use  as  a  name  for  certain  methods  of  float- 
ing minerals  in  connection  with  the  Horwood  process  mentioned  below. 
'Selective'  flotation  has  come  to  mean  (by  common  consent)  the 
flotation  of  valuable  minerals  (generally  the  metal  sulphides)  in 
the  presence  of  undesirable  gangue-minerals.  'Preferential'  flotation 
is  the  flotation  of  one  of  the  ordinary  selectively  flotative  minerals 
in  the  presence  of  another  similar  mineral.  Thus,  a  mixture  of 
galena  and  sphalerite  can  be  floated  'selectively'  from  a  gangue  of 
granite,  limestone,  or  other  common  gangue-material,  while  galena 
may  be  floated  'preferentially'  from  a  mixture  of  galena  and 
sphalerite. 

On  account  of  the  great  interest  manifested  in  this  subject  of 
late,  I  have  thought  that  the  following  review  of  proposed  or 
operating  processes  might  be  of  interest.  This  review  is  largely 
a  compilation  of  patent  literature,  but  it  might  be  well  to  call 
attention  to  the  fact  that,  at  present,  patent  literature  is  one  of 
the  best  sources  of  information  on  the  subject  of  flotation  for  one  who 
does  not  have  the  opportunity  to  visit  at  first-hand  the  localities  where 
the  practice  of  flotation  is  being  used  or  tested. 

CATTERMOLE.  In  1904  Cattermole  (U.  S.  Patent  763,259)  made 
one  of  the  earliest  proposals  for  the  preferential  flotation  of  minerals. 
The  method,  as  he  described  it,  was  not  exactly  a  flotation  method, 
but  it  involved  most  of  the  underlying  principles  of  flotation,  and 
hence  is  of  interest  in  this  connection.  As  stated  by  Cattermole: 
"The  invention  relates  to  the  classification  of  the  metalliferous  con- 
stituents of  ores  which  have  been  separated  from  gangue  by  oil  or 
similar  matter,"  and  "consists  in  fractionally  removing  the  different 
constituents  from  the  agglomerated  masses  by  freeing  the  constituents 
in  turn  from  oil,  and  thus  obtaining  them  in  a  separable  condition 
by  the  use  of  emulsifying  agents  of  varying  strength  and  activity, 
preferably  in  conjunction  with  an  alkali."  "In  carrying  out  the 


*Contributed  by  the  Department  of  Metallurgical  Research,  University 
of  Utah.  D.  A.  Lyon,  metallurgist  in  charge;  O.  C.  Ralston,  assistant  metal- 
lurgist. Published  by  permission  of  the  Director  of  the  U.  S.  Bureau  of  Mines. 


72  THE  FLOTATION   PROCESS 

process,  the  metalliferous  matter  agglomerated  by  oil  is  mixed  and 
agitated  with  a  solution  of  an  emulsifying  agent,  such  as  a  soluble 
soap-alkaline  oleate,  for  example,  to  which  a  certain  proportion  of 
soluble  alkali,  preferably  caustic  potash  or  soda,  has  been  added." 
* '  It  is  found  that  the  minerals  vary  in  their  affinity  for  oil  employed 
in  the  above  manner,  and  thus  by  treating  the  oily  masses  or 
granules  in  the  first  place  with  an  alkaline  emulsifying  solution  of 
a  certain  strength,  the  mineral  of  least  affinity  can  be  separated 
therefrom,  and  by  increasing  the  strength  or  modifying  the  propor- 
tions of  the  breaking  down  solution  step  by  step,  the  various  con- 
stituents can  be  thrown  out  in  the  order  of  their  increasing  affinity. ' ' 

Cattermole's  patent  came  at  a  time  when  the  process  was  truly 
'oil  flotation,'  as  the  use  of  small  amounts  of  oil  had  not  been  made 
successful,  and  the  particular  method  of  flotation  which  he  had  in 
mind  in  this  patent  was  probably  that  described  in  one  of  his  other 
patents,  in  which  the  minerals  desired  were  flocculated  or  granulated 
by  the  use  of  oil  in  larger  amounts  than  the  present  methods  of 
flotation,  that  is,  in  amounts  up  to  5%  by  weight  of  the  ore.  and 
these  granules  would  sink  of  their  own  weight  in  an  upward 
moving  current  of  water,  such  as  that  of  a  classifier,  while  the 
unflocculated  gangue  would  rise.  He  made  the  wording  of  his  patent, 
however,  broad  enough  to  cover  the  treatment  of  products  as  obtained 
by  true  flotation. 

As  an  example  of  the  working  of  his  process  he  uses  an  ore 
consisting  of  a  silicious  gangue,  zinc-blende,  copper  pyrite,  and  galena, 
which  has  been  treated  with  an  oil  for  the  granulation  of  the  mineral 
sulphide  particles,  and  the  latter  separated.  The  oil  is  preferably 
one  that  is  not  readily  emulsified,  such  as  a  hydro-carbon  oil,  which 
will  give  a  wide  range  of  strength  in  the  solutions  used  later  in  the 
breaking  down  of  the  granules.  The  compound  granules  are  run 
into  the  first  agitation  apparatus  where  they  are  agitated  with  a 
solution  containing,  say,  0.75%  alkali,  by  which  the  zinc-blende  is 
"dropped  out."  The  remaining  granules  are  passed  into  the  next 
similar  apparatus,  in  which  a  solution  containing  1.5%  soap  and 
1.5%  alkali  is  used.  Here  the  copper  pyrite  is  freed  and  only  the 
granules  of  galena  remain.  As  Cattermole  proposed  the  use  of  so 
much  oil,  it  had  to  be  recovered  by  the  use  of  strong  alkali  solutions. 

The  rules  for  proportioning  the  solutions  took  into  account  the 
fineness  of  the  ore,  the  relative  proportions  of  the  minerals,  their 
physical  condition  and  chemical  composition,  also  the  kind  of  oil 
and  emulsifying  agents  used,  and  the  alkali  selected.  The  finer  the 


PREFERENTIAL   FLOTATION  73 

ore  the  more  compact  and  cohesive  the  granules  formed,  and  hence 
the  stronger  the  solution  required  to  break  them  down.  With  granules 
largely  of  galena,  which  breaks  down  with  difficulty,  stronger  solutions 
are  necessary  than  for  those  consisting  mainly  of  sphalerite.  With 
animal  or  vegetal  oils  that  emulsify  easily  the  breaking  down  of  the 
granules  will  be  too  rapid  for  convenience.  The  heavy  residuum 
oils  and  the  heavy  hydro-carbon  oils  are  the  best.  Oils  may  be 
blended  advantageously  for  this  purpose.  An  alkaline  solution  of 
the  oil  used  in  granulating  is  best  for  emulsifying. 

Whether  or  not  Cattermole's  process  was  ever  applied  is  not 
known  to  me,  but  it  is  not  impossible  that  its  principles  may  be 
applied  to  modern  flotation  froths. 

WENTWORTH.  Following  the  U.  S.  patents  in  their  chronological 
order,  the  next  is  No.  938,732,  of  1909,  taken  out  by  H.  A.  Wentworth 
and  assigned  to  the  Huff  Electrostatic  Separator  Co.  It  "relates 
to  the  separation  of  the  ingredients  which  constitute  ore  mixtures, 
and  particularly  to  the  separation  of  sulphide  ores  from  each  other. ' ' 
"The  process  consists  in  the  preliminary  treatment  of  ore  mixtures 
containing  several  sulphides,  which  converts  some  of  the  sulphides, 
superficially  at  least,  into  metallic  compounds  which  are  differentiated 
in  their  behavior"  with  respect  to  flotation  processes  as  commonly 
practised.  To  use  the  words  of  a  later  patentee,  the  surfaces  of 
such  minerals  as  galena,  pyrite,  and  chalcopyrite  are  'deadened7  by 
a  very  short  and  slight  roast  in  a  roasting-furnace,  while  the  sphalerite 
is  unaffected.  Thus  the  sphalerite  can  be  removed  by  flotation  from 
such  an  ore,  leaving  the  other  sulphide  minerals  to  be  removed  by 
other  means.  A  few  minutes  heating  at  a  dull-red  heat  has  been 
found  to  be  sufficient. 

This  is  a  type  of  process  that  has  been  tried  in  Australia  under 
the  name  of  the  Horwood.  It  is  further  described  under  that  heading 
in  this  paper. 

RAMAGE.  The  same  idea  underlies  the  next  patent,  which  is 
No.  949,002,  of  1910,  taken  out  by  A.  S.  Ramage  and  assigned  to  the 
Chemical  Development  Co.,  a  Colorado  corporation.  "This  process 
has  for  its  object  the  separation  of  the  valuable  minerals  from  such 
ores  as  chalcopyrite,  bornite,  or  erubescite,  and  mixtures  of  the  same 
with  pyrite,  in  which  ores  the  copper  is  in  chemical  combination 
with  the  iron;  and  also  from  such  ores  containing  zinc-blende.  The 
method  is  also  applicable  to  compound  ores,  such  as  those  of  the 
Cobalt  district  and  other  sulph-arsenides. "  "The  principle  of  the 
process  is  founded  on  the  combination  of  fractional  roasting  with 


74  THE   FLOTATION   PROCESS 

chemical  floating."  Kamage's  introduction  of  the  term  "fractional 
roasting"  is  particularly  felicitous,  as  it  more  accurately  describes 
the  method  than  does  the  term  " preferential  flotation,"  used  by 
Horwood. 

Eamage  described  the  process  by  the  use  of  three  examples,  which 
are  decidedly  interesting.  The  first  example  is  of  an  ore  containing 
iron  pyrite  and  chalcopyrite,  with  a  content  of  about  5%  copper 
and  30  to  40%  sulphur.  The  ore  is  roasted  at  about  a  red -heat  long 
enough  to  decompose  the  pyrite  slightly  and  not  affect  the  chalcopyrite. 
"The  burnt  ore  is  then  crushed  to  at  least  15  mesh  and  passed  through 
a  solution  of  acid  sulphate  of  soda  and  nitric  acid  (the  solution  being 
formed  by  adding  nitric  acid  to  sulphate  of  soda),  which  solution 
is  kept  near  the  boiling  point.  The  copper  sulphide  immediately 
rises  to  the  top  of  the  bath  and  can  be  skimmed  off."  The  copper 
dissolved  in  the  bath  can  be  recovered  in  known  ways.  This  method 
of  flotation  (hot  acid  bath)  is  not  new,  having  been  patented  by 
De  Bavay,  Potter,  Delprat,  and  others.  The  fractional  roasting  had 
been  previously  patented  by  Wentworth,  and  so  the  only  thing 
that  seems  new  is  the  combination  of  methods. 

A  second  example  is  that  of  an  ore  containing  pyrite,  chalcopyrite, 
and  zinc-blende  in  quantity.  The  ore  is  roasted  at  a  temperature  of 
not  over  600°  C.,  so  that  only  the  iron  pyrite  is  deadened.  The 
roasted  ore  is  then  subjected  to  the  acid  sulphate  of  soda  solution 
for  flotation  of  the  unchanged  sulphides  of  zinc  and  of  copper.  This 
product  is  then  roasted  at  about  700°  C.  until  all  of  the  zinc  sulphide 
is  decomposed  and  the  copper  sulphide  unchanged.  This  mixture 
is  treated  with  a  solution  of  dilute  sulphuric  acid  for  the  dissolution 
of  the  zinc,  to  be  recovered  from  solution  by  any  familiar  process, 
such  as  electrolysis,  the  copper  sulphides  being  sent  to  the  copper 
smelter.  There  are  certainly  most  interesting  facts  disclosed  in  this 
patent.  The  great  resistance  of  copper  sulphides  to  the  roasting 
process,  as  compared  with  the  sulphides  of  zinc,  is  something  new 
and  will  be  a  most  valuable  characteristic,  if  true. 

The  third  example  is  that  of  the  ores  of  the  Cobalt  district, 
Canada,  where  cobaltite,  niccolite,  chalcopyrite,  pyrite,  and  native 
silver  occur.  All  the  sulphide  and  sulph-arsenide  minerals  are  floated, 
leaving  the  silver  in  the  gangue.  The  sulphides  are  roasted  at  about 
800°  C.  and  everything  is  decomposed  except  the  copper  sulphide, 
which  can  be  floated  from  the  calcine.  Again  we  have  mention 
of  the  almost  incredible  property  of  copper  sulphides  to  resist  roasting. 

The  next  patent  was  that  of  H.  A.  Wentworth,  amplifying  on 


PREFERENTIAL.   FLOTATION  75 

his  former  patent  in  claiming  the*  superficial  chemical  change  of 
minerals  as  a  method  of  separating  them  preferentially  by  flotation. 
He  had  in  mind  particularly  the  treatment  of  the  ore  with  chlorine, 
which  would  sink  when  subjected  to  a  film-flotation  process,  while 
others  would  have  their  flotative  properties  enhanced.  As  an  example, 
a  mixture  of  zinc  and  iron  sulphides,  when  treated  with  chlorine  gas 
in  a  slightly  damp  state,  is  so  altered  that  the  blende  will  float  on  a 
film-flotation  machine  much  better  than  before  treatment,  while 
the  pyrite  has  a  coating  formed  over  its  surface,  which  is  much 
more  easily  wetted,  so  that  it  will  sink.  Still  a  further  example  is 
the  application  to  the  separation  of  pyrite  and  chalcopyrite.  The  latter 
is  attacked  much  slower  than  pyrite;  hence  it  can  be  floated  when 
both  are  present.  A  similar  behavior  of  the  minerals  is  observed  when 
they  are  suspended  in  water  containing  dissolved  chlorine  in  the 
proper  concentration,  but  the  best  work  seems  to  be  done  with 
minerals  fed  onto  one  of  the  film-flotation  machines,  such  as  that  of 
H.  E.  "Wood  of  Denver,  although  Wentworth  gives  the  design  of  one 
of  his  own  in  the  specification.  It  is  easy  to  see  that  with  chlorine- 
water  and  one  of  the  mechanical  frothing  methods  of  flotation  the 
soluble  coatings  that  are  formed  on  the  surfaces  of  the  minerals 
would  be  simply  washed  off  and  the  preferential  part  of  the  flotation 
lost.  Tests  in  our  laboratory  seem  to  show  this.  So  far  as  is  known 
to  me,  this  process  is  not  being  used. 

HORWOOD.  This  process  of  preferential  flotation  is  practically  the 
same  as  that  described  under  Wentworth  and  Ramage.  It  has  been 
worked  for  some  years  in  Australia  and  received  careful  testing 
by  the  Zinc  Corporation.  It  depends  upon  the  '  deadening '  of  galena 
and  pyrite  in  a  short  roasting  at  300  to  500°  C.,  whereby  the  galena 
is  coated  with  lead  sulphate  and  the  pyrite  with  iron  oxide,  while 
the  sphalerite  is  unaltered.  This  allows  a  separation  of  the  undesirable 
zinc  from  the  lead-iron-silver  product  and  allows  their  separate 
marketing.  This  process  has  received  more  careful  attention  than 
any  other  process,  and  reference  to  original  articles  is  best.f  Accord- 
ing to  the  data  given  in  some  of  this  literature,  it  appears  that 
it  is  possible  to  take  a  flotation  concentrate  containing  36%  Zn,  15% 
Pb,  and  22  oz.  Ag  per  ton,  and  divide  it  into  a  zinc  product 
running  as  high  as  50%  Zn,  7%  Pb,  and  15  oz.  Ag,  and  a  lead 


fT.  J.  Hoover,  'Concentrating  Ores  by  Flotation';  Min.  &  Eng.  World,  July 
18,  1914,  p.  96;  Eng.  &  Min.  Jour.  (1914),  97,  p.  1208;  Mining  and  Scientific 
Press,  April  18,  1914,  p.  657;  Metal.  &  Chem.  Eng.  (1914),  No.  12,  p.  350 
and  592. 


76  THE  FLOTATION   PROCESS 

product  containing  38%  Pb,  8%.  Zn,  and  42  oz.  Ag  per  ton.  This 
is  of  great  interest  to  all  producers  of  'complex  sulphide'  ores,  as 
the  milling  of  coarsely  crystalline  material  has  presented  much 
difficulty  in  the  past  for  the  reason  that  some  finely  divided  material 
(slime)  is  bound  to  form  in  crushing,  and  while  the  combined  lead 
and  zinc  sulphides  can  be  floated  nowadays  without  much  difficulty, 
the  mixture  is  of  far  less  value  than  the  two  minerals  separated. 
This  is  important  enough,  not  to  speak  of  the  possibility  of  treating 
the  microcrystalline  sulphide  ores  and  those  containing  gangue  of 
high  specific  gravity,  such  as  barite.  While  flotation  has  been  a 
boon  to  the  concentration  of  all  sulphide  slimes,  preferential  flotation 
is  much  more  important  for  the  ores  containing  undesirable  com- 
binations of  sulphides.  Hence  Horwood's  work  should  receive  the 
highest  praise. 

Another  detail,  as  regards  this  process,  is  that  35  Ib.  of  sulphuric 
acid  per  ton  of  ore  is  necessary  and  2  to  3  Ib.  of  oleic  acid  for  the 
flotation  of  the  unaltered  zinc.  All  of  this  appeared  in  Horwood's 
first  patent,  No.  1,020,353,  of  1912,  and  he  later  came  out  with 
improvements  on  the  process  in  patent  No.  1,108,440,  of  1914.  In 
this  later  patent  he  stated  that  he  had  found  there  was  a  tendency 
for  the  silver  to  follow  the  zinc,  which  is  undesirable,  but  that  this 
could  be  prevented  by  simply  washing  away  all  soluble  salts  on 
the  concentrate  before  it  was  subjected  to  the  deadening  roast.  This 
reduces  the  amount  of  oxidized  zinc  formed,  and  lost  by  solution  in 
the  dilute  acid  in  the  mill-water,  as  well  as  allowing  the  silver  to 
become  deadened  to  a  greater  extent.  He  also  found  that  the  most 
successful  flotation  took  place  with  the  pulp  at  a  temperature  of 
about  120°  F. 

It  will  be  seen  that  the  Horwood  process  has  been  applied  only 
to  concentrates  from  previous  flotation  or  from  other  concentration 
processes.  This  is  the  logical  place  to  apply  it,  as  there  is  no  object 
in  leaving  a  non-flotative  galena  or  other  sulphide  mixed  with 
gangue,  by  using  the  process  on  crude  ore.  The  same  remark  applies 
to  many  of  the  other  processes.  To  be  sure,  there  has  been  some 
success  in  the  Australian  mills  as  well  as  in  the  United  States  in 
the  treatment  of  mixed  galena-sphalerite  concentrates  from  flotation 
machines  on  concentrating  tables.  As  an  example,  the  Timber  Butte 
mill  is  treating  the  flotation  concentrate  of  a  zinc  ore  containing 
some  zinc  concentrate  carrying  53%  Zn,  1.5%  Pb,  and  4%  insoluble. 
However,  this  method  has  not  always  met  with  the  best  results, 
and  where  the  proportions  of  lead  and  zinc  in  ordinary  complex 


PREFERENTIAL   FLOTATION  77 

sulphide  concentrates  are  about  equal  it  is  quite  hard  to  get  two 
products  that  are  sufficiently  pure.  Where  it  can  be  done,  it  is 
certainly  more  desirable  than  the  more  complex  fractional  roasting 
and  preferential  flotation  processes  of  Horwood,  Wentworth,  and 
Ramage. 

LYSTER.  This  is  another  process  that  has  received  consideration 
by  the  Zinc  Corporation  for  the  year  or  two  preceding  the  European 
war.  Lyster's  process  is  carried  on  in  neutral  or  alkaline  solutions 
(never  acid)  of  the  sulphates,  chlorides,  or  nitrates  of  calcium, 
magnesium,  sodium,  potassium,  or  of  their  mixtures,  or  solutions 
of  manganese,  zinc,  iron,  acid  sodium,  or  sodium-potassium  sulphates. 
Using  eucalyptus  oil  or  a  similar  frothing  agent,  the  agitation  of  the 
pulp  takes  place  in  centrifugal  pumps,  throttled  to  give  further 
agitation,  and  discharging  into  spitzkasten  with  constricted  tops. 
It  is  said  that  a  galena  froth  can  be  collected  carrying  55  to  60% 
lead  and  that  by  sending  the  tailing  to  a  second  machine  with 
further  addition  of  oil,  the  sphalerite  can  be  floated. 

It  will  be  noticed  that  this,  with  the  possible  exception  of  Went- 
worth's  second  patent,  is  one  of  the  first  proposals  to  give  a  true 
' preferential'  flotation  to  a  mixture  of  sulphides,  as  the  roasting 
methods  above  mentioned  involve  an  actual  conversion  of  some  of 
the  minerals,  so  that  sulphide  surfaces  are  no  longer  presented  to  the 
oils  and  air  bubbles  in  the  flotation  operation.  Lyster's  process, 
however,  involves  the  actual  flotation  of  one  mineral  in  preference 
to  another,  unless  the  chemicals  used  are  chemically  altering  certain 
of  the  sulphides  so  that  they  cannot  float.  Anyone  who  has  worked 
with  mixtures  of  sulphides  has  doubtless  noticed  that  greater  care 
is  necessary  in  the  flotation  of  zinc  sulphide  than  in  floating  galena; 
in  fact,  galena  is  one  of  the  most  easily  floated  minerals  outside  of 
molybdenite,  and  zinc  sulphide  is  considerably  more  difficult.  The 
fact  that  a  froth  running  so  high  in  lead  as  the  Lyster  process  is 
reported  to  give  would  also  tend  to  make  one  suspicious  that  rather 
poor  flotation  conditions  are  maintained,  so  that  only  the  most  easily 
floated  material  (galena),  and  only  the  purest  of  that,  is  coming 
up  in  the  first  product.  This  takes  place  even  in  the  presence  of 
considerable  oil,  whenever  flotation  conditions  are  poor  on  almost 
any  type  of  machine,  and  while  the  grade  of  froth  that  is  obtained 
is  high,  the  extraction  is  poor  on  account  of  the  fact  that  only  the 
best  mineral  is  floating.  It  is  possible  that  some  such  combination 
of  results  as  this  has  caused  the  process  not  to  be  considered 
Unfavorably. 


78  THE  FLOTATION   PROCESS 

NUTTER  AND  LAYERS.  Perhaps  the  most  important  disclosure  of 
a  process  for  preferential  flotation  of  minerals  is  contained  in  the 
patent  specifications  taken  out  by  E.  H.  Nutter  and  H.  Lavers, 
U.  S.  Patent  No.  1,067,485  of  1913.  This  patent  was  assigned  to 
Minerals  Separation,  Limited,  as  the  patentees  are  engineers  in  the 
employ  of  that  company.  The  wording  of  the  patent  shows  more 
actual  contact  with  flotation  work  on  the  part  of  the  patentees  than 
perhaps  any  other  single  patent  that  has  been  granted.  They  have 
observed  that  while  controlling  conditions  in  a  flotation  plant,  the 
varying  of  certain  of  these  conditions  has  been  accompanied  by 
changes  in  the  character  of  the  froth  coming  off  their  machines, 
the  metals  coming  off  in  various  ratios  to  each  other  at  different 
times,  and  for  definite  causes.  Thus  there  is  considerable  difference 
in  the  sizes  of  the  different  minerals  separated  under  various 
conditions.  It  is  no  uncommon  experience  while  developing  the 
machinery  of  a  flotation  mill  to  float  all  of  the  fine  part  of  the 
gangue  as  well  as  the  sulphide  minerals.  In  like  manner,  the  more 
easily  flotative  minerals  are  liable  to  come  off  in  the  first  froth  that 
issues  from  a  machine  accompanied  by  the  more  finely  divided 
portions  of  the  less  easily  flotative  minerals.  "This  tendency  is 
dependent  upon  several  factors,  such  as  the  amount  and  character 
of  the  agitation  and  aeration,  or  of  each  singly,  the  chemical 
constitution  of  the  solution  employed  as  mill-water,  the  degree  of 
dilution,  the  temperature  and  the  amount  and  nature  of  the  different 
frothing  agents. "  "The  word  aeration  is  used  in  this  specification 
to  mean  the  supplying  of  air  or  other  gas  or  gases. "  By  sufficiently 
controlling  all  of  these  factors  it  is  possible  to  obtain  effective 
separation  of  galena  and  sphalerite  as  well  as  other  sulphides  and 
metals.  By  taking  the  various  froths  obtained  from  subjecting  the 
pulp  to  varying  conditions,  and  classifying  on  apparatus  such  as 
concentrating  tables  it  is  often  possible  to  get  good  separation  of 
the  minerals  contained. 

One  example  cited  is  that  of  an  ore  containing  sulphides  of  lead, 
copper,  and  zinc.  From  this  can  be  obtained  a  froth  containing 
most  of  the  chalcopyrite,  and  not  much  of  the  galena  or  the  sphalerite, 
by  the  use  of  cresylic  acid  (cresol)  without  the  addition  of  mineral 
acid  to  the  pulp.  This  froth  can  be  re-treated  under  varying  con- 
ditions to  purify  it.  To  the  mill-pulp  that  has  been  depleted  of  its 
copper  can  be  added  sulphuric  acid  as  well  as  the  frothing  agent, 
to  obtain  the  major  portion  of  the  lead,  and,  finally,  by  the  addition 
of  such  an  oil  as  oleic,  it  is  possible  to  float  all  of  the  zinc  mineral, 


PREFERENTIAL   FLOTATION  79 

as  well  as  any  coarse  particles  of  chalcopyrite  and  galena.  The 
re-treatment  of  these  froths  by  further  flotation,  or  on  tables,  makes 
it  possible  to  get  good  products  of  the  grade  demanded  by  smelters. 

When  using  an  ore  containing  only  copper  and  zinc  sulphides 
they  state  that  with  the  use  of  cresylic  acid  or  eucalyptus  oil,  without 
the  addition  of  any  mineral  acid,  it  is  possible  to  get  a  froth 
containing  a  portion  of  the  copper  minerals,  some  fine  zinc,  and 
some  still  finer  gangue.  They  also  state  that  if  the  remaining  pulp 
is  acid,  the  froth  obtained  will  contain  an  additional  amount  of 
more  coarse  zinc  and  copper  minerals  and  that  the  zinc  minerals 
are  finer  than  the  copper  minerals.  If  oleic  acid  is  added  to  clean 
the  tailing,  the  froth  obtained  will  carry  much  gangue,  but  most 
of  the  sphalerite  and  chalcopyrite  are  very  coarse-grained.  The 
treatment  of  these  froths  on  vanning  machines  or  tables  gives  the 
desired  products. 

Consciously  or  unconsciously,  a  number  of  operators  have  applied 
methods  more  or  less  like  those  claimed  in  this  patent.  By  restricting 
the  amount  of  oil  used,  it  seems  to  be  possible  to  float  galena  in  the 
presence  of  sphalerite,  though  the  lead  product  obtained  always 
carries  a  good  deal  of  zinc,  and  it  is  impossible  to  get  all  of  the 
lead  out  before  the  sphalerite  is  floated  by  the  addition  of  further 
oil.  This  is  practically  an  application  of  Lyster's  process,  except 
that  pure  water  is  used  instead  of  the  solutions  recommended  by 
him.  However,  there  can  be  no  doubt  that  the  addition  of  certain 
substances  to  the  mill-water  does  help  in  this  type  of  flotation. 
In  another  plant  where  an  ore  containing  pyrite  and  chalcopyrite 
is  being  treated,  the  first  froth  contains  most  of  the  chalcopyrite  in 
a  finely  divided  form,  while  only  a  small  amount  of  the  pyrite,  in 
large  pieces,  comes  to  the  surface.  The  property  of  chalcopyrite 
to  disintegrate  into  very  fine  flakes  on  crushing  has  bothered  mill- 
men  in  the  old  days  when  the  production  of  slime  was  kept  down 
to  a  minimum.  Now  it  seems  to  be  an  advantage.  These  two 
instances  of  "controlling  flotation "  conditions  are  somewhat  different 
from  the  ones  implied  in  the  Nutter  and  Lavers  patent,  and  it  is 
doubtful  if  it  could  be  held  to  cover  these  cases,  at  least  more  than 
in  part.  However,  too  much  attention  cannot  be  given  to  their 
patent,  as  it  discloses  the  methods  by  which  preferential  flotation 
will  be  first  developed  successfully,  as  far  as  I  am  able  to  see. 

GREENWAY  AND  LOWRY.  A  further  development  of  the  idea  of 
using  a  solution  of  some  chemical  that  will  permit  true  preferential 
flotation  of  one  mineral  in  the  presence  of  another  flotative  mineral 


80  THE   FLOTATION   PROCESS 

is  contained  in  the  patent  of  H.  H.  Greenway  and  A.  H.  P.  Lowry, 
No.  1,102,738  of  1914.  They  discovered  that  "if  a  salt  of  chromium 
(such  as  sodium  bichromate  or  potassium  bichromate)  is  introduced 
in  solution  into  the  circuit  liquors,  or  if  the  material  to  be  treated 
is  subjected  to  the  action  of  such  chromium  salt  solution  by  digestion 
or  otherwise,  the  sulphides  are  affected  in  such  a  way  as  to 
leave  certain  of  them  amenable  to  flotation,  whereby  products  are 
obtained  relatively  high  in  certain  sulphides  on  the  one  hand,  and 
relatively  high  in  the  other  sulphides  on  the  other." 

Three  examples  are  cited:  (1)  A  molybdenum  ore  containing 
15%  molybdenite  and  25%  iron  pyrite  was  crushed  to  pass  100-mesh 
screen  and  treated  in  a  froth-flotation  apparatus  with  four  times 
its  weight  of  water  containing  0.25%  sodium  bichromate,  and  heated 
to  120°  F.  One  pound  of  eucalyptus  oil  per  ton  of  slime  was 
used  and  the  flotation  product  consisted  of  93%  MoS2  and  4.9% 
iron  pyrite.  Attention  should  be  called  to  the  fact  that  this  example 
does  not  tell  as  much  as  it  would  seem  to  say,  for  the  reason  that 
molybdenite  is  one  of  the  most  easily  floated  minerals.  I  believe 
that  work  of  a  character  more  nearly  comparable  with  this  result 
could  be  obtained  without  the  use  of  chromates. 

The  second  example  cited  is  of  a  copper  ore  containing  6.5% 
copper  and  35%  iron.  This,  likewise,  was  crushed  to  pass  a  100-mesh 
screen  and  digested  in  a  hot  solution  of  1%  sodium  chromate  for 
about  30  minutes,  the  liquor  decanted  and  the  mineral  treated  in 
a  flotation  machine  with  one  pound  of  eucalyptus  oil  per  ton  of 
dry  slime.  The  flotation  product  contained  19%  copper  and  30.2% 
iron,  while  the  residue  contained  0.7%  copper  and  36.2%  iron.  When 
we  remember  the  case  cited  above  of  separating  the  chalcopyrite 
from  the  pyrite  by  virtue  of  the  fact  that  fine  grinding  takes  the 
copper  down  to  a  much  finer  product  than  it  does  the  iron,  we 
are  led  to  wonder  if  this  process  is  really  necessary  for  this  kind 
of  ore.  It  may  be  that  a  better  grade  of  product  and  a  higher 
extration  can  be  obtained  by  this  method  than  without  the  addition 
of  bichromate,  but  otherwise  it  is  doubtless  possible  in  most  cases 
to  do  the  same  work  with  proper  control  of  ordinary  conditions. 

Their  third  example  is  of  a  lead-zinc  slime  containing  18.6%  lead 
and  32.3%  zinc,  which  was  digested  for  30  minutes  in  a  warm  solution 
of  1%  sodium  bichromate.  The  solution  was  decanted  and  the 
material  subjected  to  froth-flotation  with  one  pound  of  eucalyptus 
oil  per  ton  of  slime.  The  flotation  product  contained  47.2%  zinc 
and  6%  lead,  while  the  residue  contained  31.6%  lead  and  16.3% 


PREFERENTIAL    FLOTATION  81 

zinc.  The  solution  was  heated  to  120°  C.  These  are  interesting 
figures,  but  there  is  too  much  zinc  in  the  lead  concentrate.  Here 
again  I  feel  that  the  work  is  not  much  better  than  it  would  be 
without  the  aid  of  bichromates.  By  taking  advantage  of  the  fact 
that  galena  floats  more  easily  than  blende,  it  is  possible  to  get  a 
galena  froth  from  an  ore  that  will  contain  54%  lead  and  15% 
zinc,  while  the  blende-froth  that  follows  will  contain  37%  zinc  and 
20%  lead.  This  type  of  work  errs  in  the  other  direction,  that  is, 
in  having  too  much  lead  in  the  zinc  product,  but  the  point  is  that 
the  addition  of  bichromates  does  not  make  a  separation  which  is 
any  more  advantageous  than  does  preferential  flotation  by  other 
methods.  However,  the  fact  that  the  galena  can  be  deadened  by 
treatment  with  a  weak  solution  of  sodium  bichromate  is  most 
interesting  in  that  it  shows  that  a  true  preferential  flotation  is 
possible.  It  is  assumed  that  the  action  of  the  bichromate  solution 
must  be  that  of  oxidation  of  the  surfaces  of  the  galena  to  insoluble 
sulphate,  while  such  an  action  on  the  sphalerite  could  not  be  possible, 
as  the  zinc  sulphate  would  dissolve.  The  treatment  of  the  high 
lead-zinc  product  of  this  last  mentioned  preferential  flotation  product 
by  the  bichromate  process  might  be  a  useful  method  of  cleaning  this 
kind  of  concentrate.  It  is  probable  that  successful  preferential 
flotation  will  develop  along  such  lines,  though  bichromates  are  not 
the  only  chemicals  that  will  be  used.  While  the  results  obtained 
by  this  process  have  been  shown  to  be  capable  of  duplication  other- 
wise than  by  the  use  of  bichromates,  this  fact  of  the  peculiar  action 
of  weak  bichromate  solutions  is  thankfully  accepted  and  further  work 
is  urged  to  discover  if  it  can  have  a  field  of  application  peculiarly 
its  own. 

BRADFORD.  Another  process  along  these  lines  is  that  revealed  in 
British  Patent  No.  21,104  of  1913,  by  L.  Bradford  of  Broken  Hill. 
He  claims  the  use  of  a  solution  that  will  wet  one  of  the  sulphides 
which  it  is  desired  to  separate  from  the  other  preferentially  without 
chemically  altering  the  same.  A  medium  which  will  wet  galena 
particles  and  allow  sphalerite  and  pyrite  to  float  unaffected  is  a 
solution  of  one  or  more  of  the  alkaline  chlorides,  slightly  acidulated 
and  heated  to  about  120  to  160°  F.  On  account  of  its  low  cost  a 
solution  of  sodium  chloride  is  used,  and  Bradford  states  that  there 
are  no  definite  requirements  as  to  how  concentrated  the  solution  shall 
be,  but  suggests  a  10%  NaCl  solution  as  about  the  right  strength 
to  use. 

The  acidity  should  be  about  0.1  to  0.2%,  for  a  higher  amount 


82  THE  FLOTATION   PROCESS 

than  \%  will  cause  the  flotation  of  galena  on  account  of  the 
formation  of  hydrogen  sulphide  bubbles  on  its  surface.  He  states 
that  if  the  process  is  applied  directly  to  crude  ores  the  use  of  a 
frothing  agent  is  not  necessary,  although  it  will  cause  no  harm  if 
added.  Any  well-known  apparatus  can  be  used  for  the  flotation. 

The  invention  may  be  applied  either  to  the  crude  ore  or  to  the 
mixed  flotation  concentrate  from  the  ordinary  method  of  flotation. 
Where  the  plant  is  used  on  crude  ore  the  tailings  from  the  flotation 
of  the  sphalerite  and  the  pyrite  are  agitated  again  in  pure  water 
with  a  frothing  agent  in  order  to  float  the  galena.  On  account  of 
this  requirement  it  is  thought  better  to  make  a  mixed  concentrate 
first  by  ordinary  flotation  and  then  separate  preferentially  as  above 
described.  This  latter  method,  however,  makes  a  higher-grade  zinc 
concentrate. 

When  treating  ordinary  mixed  flotation  concentrate,  it  is  best 
to  remove  the  oil  on  the  surface  by  the  use  of  an  alkaline  or  an 
alkaline  carbonate  solution,  or  by  either.  Further,  finely  ground 
material  is  liable  to  agglomerate  too  quickly,  so  that  some  of  the 
galena  will  be  entrained  mechanically  with  the  agglomerated 
sphalerite  and  decrease  its  value.  In  these  cases  it  is  desirable  to 
add  an  agent  that  will  retard  flotation.  Substances  suitable  for 
this  purpose  are  sulphites  or  thiosulphites  of  alkalies  or  sulphur 
.dioxide,  but  they  must  be  used  sparingly  and  with  care,  or  they 
will  entirely  spoil  all  flotation.  He  thought  so  much  of  this  latter 
step  that  he  later  incorporated  it  in  a  separate  patent  (Brit.  Pat. 
No.  19,844  of  1914.)  No  further  description  of  this  patent  is 
necessary. 

There  are  many  other  proposed  methods  in  the  patent  literature 
of  England,  Germany,  France,  and  the  United  States,  concerning 
which  I  am  not  fully  informed,  but  it  is  believed  that  most  of 
the  important  ones  have  been  reviewed.  Many  interesting  details  are 
disclosed,  such  as  the  fact  that  galena  and  sphalerite  will  not  float 
in  a  solution  containing  zinc  chloride  of  the  right  concentration  and 
acidified  by  hydrochloric  acid  (German  patent,  No.  282,234).  Aniline 
compounds  are  said  to  allow  flotation  of  galena  in  preference  to 
sphalerite,  etc. 

It  will  doubtless  be  noticed  that  little  mention  is  made  of  the 
kinds  of  machinery  used  in  the  above  methods  of  preferential  flotation 
and  there  will  doubtless  be  some  question  as  to  whether  or  not  these 
principles  can  be  applied  equally  well  in  the  mechanically-agitated 
and  in  the  pneumatic-agitation  machines.  Most  of  the  above  processes. 


FLOTATION  AT  THE  INSPIRATION  MINE,  ARIZONA  83 

where  not  specifically  stated,  have  been  worked  out  with  the  aid  of 
mechanically-agitated  machines,  but  it  is  possible  to  apply  most 
of  them  to  the  penumatically-agitated  machines,  such  as  the  Callow 
or  the  Towne.  Such  machines,  owing  to  the  economy  of  power  in 
making  froth,  and  the  easy  control  of  flotation  conditions,  will 
doubtless  materially  assist  in  the  development  of  preferential 
flotation. 


FLOTATION  AT  THE  INSPIRATION  MINE,  ARIZONA 

By  WILLIAM  MOTHERWELL 
(From  the  Mining  and  Scientific  Press  of  July  3,  1915) 

The  Inspiration  Consolidated  Copper  Co.'s  mine  near  Miami,  in 
Arizona,  is  estimated  to  contain  97,143,000  tons  of  1.63%  copper 
ore,  mostly  in  the  form  of  chalcocite.  The  ore  at  present  being  mined 
contains  about  0.20%  metal  in  the  form  of  carbonate  and  silicate. 

For  some  time  past  the  company  has  been  experimenting  with 
a  view  to  finding  the  best  method  of  concentrating  the  sulphide  ore 
before  smelting.  The  first  test-mill  consisted  of  two  sets  of  rolls, 
one  Chilean  mill,  one  Hardinge  conical  mill  6  ft.  diam.  by  12  in. 
cylinder,  Richards  hindered-settling  classifier,  Deister  tables,  some 
kind  of  vanner,  and  a  50-ton  Minerals  Separation  flotation  machine 
of  standard  type  (Hoover's  single-level  apparatus).  This  mill  was 
situated  close  to  the  Joe  Bush  shaft,  on  top  of  the  orebody,  and  is 
now  dismantled.  It  is  understood  that  good  results  were  obtained. 

On  a  change  of  management  taking  place,  a  new  test-mill  was 
erected  near  the  old  leaching  plant  of  the  Black  "Warrior  Copper  Co., 
about  1J  miles  from  the  new  twin-shafts  through  which  all  ore  will 
be  hoisted  when  the  large  mill  is  running.  This  mill  will  be  the 
largest,  or  rather  will  handle  the  largest  tonnage,  of  any  mill  in 
the  world,  namely,  15,000  tons  per  day.  It  adjoins  the  test-mill 
as  can  be  seen  in  the  photograph  published  in  the  Mining  and  Scien- 
tific Press  of  May  29.  The  crushing  and  concentrating  capacity 
of  the  test-mill  is  about  1000  tons  per  day,  but  it  is  limited  by  the 
capacity  of  the  classifiers,  elevators,  etc. 

The  ore  is  at  present  hoisted  through  the  Scorpion  shaft  and 
broken  in  a  'K'  Gates  crusher  close  to  the  shaft.  From  there  it  is 
conveyed  to  the  30,000-ton  flat-bottomed  steel  and  concrete  bins 


84  THE   FLOTATION   PROCESS 

attached  to  the  crusher-station  at  the  new  shafts.  It  is  then  trans- 
ported to  the  test-mill  in  Ingoldsby  dump-cars  (each  having  a 
capacity  of  60  tons)  drawn  by  steam-locomotives  on  a  standard-gauge 
railway.  A  part  of  the  new  mill-bins  (which  are  of  steel  and  trough- 
shaped)  is  set  aside  for  the  use  of  the  test-mill.  On  leaving  these 
bins  the  ore  falls  upon  a  tray-conveyor,  then  to  an  inclined  rubber- 
belt  conveyor,  where  it  is  automatically  weighed.  At  the  head  of 
this  conveyor  there  is  a  magnetic  pulley  that  removes  pieces  of 
iron  and  steel  which  may  have  got  mixed  with  the  ore.  At  this 
point  there  is  a  grizzly  and  a  36-in.  Symons  vertical-disc  crusher. 

From  here  an  incline-conveyor  carries  the  ore  to  the  top  of  the 
test-mill,  where  it  is  divided  into  two  streams,  one  going  to  a  shaking 
screen  from  which  the  oversize  falls  into  a  48-in.  Symons  horizontal- 
disc  crusher,  where  it  is  crushed  dry,  and  the  other  to  a  5  ft.  6  in. 
by  8  ft.  diam.  Marcy  ball-mill,  where  it  is  crushed  wet  without 
previous  screening.  The  product  of  the  Symons  machine  is  fed 
to  pebble-mills  without  any  classification,  being  distributed  in  varying 
proportions  by  a  mechanical  device.  This  consists  of  a  fixed  hori- 
zontal circular  vessel  103  inches  in  circumference,  divided  into  four 
sections  by  vertical  sheet-iron  partitions  that  can  be  adjusted  to 
give  segments  of  any  size,  thus  varying  the  feed  to  each  mill  as 
desired.  By  measuring  the  number  of  inches  of  circumference  given 
to  each  division  the  proportion  of  feed  going  to  each  mill  can  be 
calculated.  Above  this  receptacle  there  is  a  vertical  crooked  revolving 
iron  pipe  through  which  the  feed  comes  from  the  Symons  machine 
after  being  mixed  with  water.  The  revolution  of  the  feed-pipe  causes 
the  pulp  to  be  discharged  into  each  division  of  the  distributor  in 
turn.  In  the  bottom  of  each  division  is  a  hole  through  which  the 
feed  passes  to  launders  leading  to  the  pebble-mills. 

The  following  kinds  of  pebble-mills  are  installed: 

1.  One  20  by  6-ft.  Chalmers  &  Williams  quick-discharge  tube- 
mill  with  herring-bone  gear  engaging  with  pinion  on  a  shaft  directly 
driven  through  a  flexible  coupling  by  an  electric  motor. 

2.  One  Hardinge  conical  mill,  10  ft.  diam.,  with  cylindrical  part 
28  in.  long  driven  through  spur  and  pinion  by  two-belt  transmission 
from  motor. 

3.  One  Hardinge  conical  mill,  8  ft.  diam.,  with  cylinder  72  in. 
long,  with  herring-bone  gear  engaging  with  pinion  on  shaft  direct 
driven  by  motor. 

4.  One  Hardinge  conical  mill,  8  ft.  diam.,  with  cylinder  36  in. 
long,  driven  in  the  same  manner  as  No.  3. 


FLOTATION  AT  THE  INSPIRATION  MINE,   ARIZONA  85 

5.  One  Hardinge  conical  mill,  8  ft.  diam.,  with  cylinder  44  in. 
long,  driven  in  same  way  as  No.  3  and  4. 

Both  silex  and  El  Oro  linings  were  tried  in  the  cylindrical  part, 
and  pebbles  set  in  cement  in  the  conical  part;  and,  in  one  mill, 
steel  plates,  which,  however,  did  not  last  long. 

Each  pebble-mill  has  a  drag-classifier  attached,  and  the  oversize 
in  the  product,  except  in  the  case  of  the  tube-mill,  is  returned  by  a 
bucket-elevator  to  the  mill  from  which  it  came.  In  the  case  of 
the  tube-mill  the  oversize  is  returned  to  the  mill  by  the  drag-classifier, 
which  is  paralled  with  the  mill.  Both  Danish  and  California  pebbles 
have  been  tried. 

The  product  of  the  Marcy  ball-mill  is  classified  in  a  duplex  Dorr 
classifier,  and  the  oversize  returned  to  the  same  machine.  This, 
as  a  fine  crusher,  has  a  capacity  of  about  13  tons  per  hour.  Of 
the  final  product  only  about  1%  remains  on  a  48-mesh  screen.  The  mill 
is  simply  a  strongly  built  cylinder  supported  on  trunnions,  contains 
about  10  tons  of  chrome-steel  or  manganoid  balls,  and  is  revolved 
at  22  r.p.m.  It  was  formerly  fed  through  the  trunnion,  then  three 
scoops  were  attached,  but  now  one  large  scoop  is  used.  It  is  lined 
with  manganese-steel  plates  and  driven  through  spur  and  pinion 
by  belting  from  a  200-hp.  motor,  using  about  140  kilowatts.  The 
discharge  is  at  the  opposite  end  to  the  feed-inlet  and  passes  through 
grates  composed  of  steel  bars  placed  close  together.  The  discharge 
area  is  more  than  half  the  entire  end  of  the  mill.  It  will  thus  be 
seen  that  it  differs  essentially  from  the  Krupp  ball-mill,  in  which 
the  screens  are  placed  around  the  periphery:  and  the  pulp  has  to 
pass  through  two  screens  before  escaping.  The  pulp  leaving  the 
ball-mill  contains  about  40%  of  moisture.  This  is  diluted  before 
entering  the  Dorr  classifier.  The  overflow  from  the  classifier  consists 
of  2^  to  3  parts  of  water  to  one  of  ore. 

The  power  required  to  drive  these  different  mills,  their  capacity, 
consumption  of  balls,  pebbles,  and  liners  are,  of  course,  known  only 
to  the  management,  but  it  is  significant  that  in  the  new  mill  all 
crushing  will  be  done  by  Marcy  mills. 

Among  other  crushing  machines  that  have  been  tried  are  the 
Bradley  roller-mill,  Symons  roller-mill,  Overstrom  mill,  and  Allis- 
Chalmers  hammer-mill.  No  rolls  or  Chilean  mills,  Krupp  mills,  or 
Marathon  mills  were  tried  in  this  plant. 

The  products  of  the  Marcy  mill,  and  such  of  the  pebble-mills  as 
are  running,  are  united  and  elevated  sufficiently  high  to  flow  to  all 
the  flotation  plants  without  undergoing  any  preliminary  table  or 


86  THE  FLOTATION   PROCESS 

vanner  concentration.  The  feed  is  distributed  to  the  flotation  plants 
in  the  following  way :  It  flows  into  the  centre  of  a  horizontal,  circular, 
revolving  apparatus  of  sheet-iron  divided  into  five  concentric  circles 
or  rings.  Each  circle  has  20  holes  in  the  bottom,  and  the  proportion 
of  feed  to  each  flotation  plant  is  regulated  by  opening  the  proper 
number  of  holes  and  allowing  the  pulp  to  enter  a  launder  along 
which  it  flows  to  the  flotation  plant.  Thus  if  the  ring  that  receives 
the  feed  intended  for  one  particular  plant  has  15  holes  plugged  and 
5  open,  this  plant  is,  of  course,  receiving  25%  of  the  total  feed,  and 
the  actual  tonnage  passed  through  it  can  be  calculated. 

Automatic  samplers,  worked  by  a  water  balance,  are  used  through- 
out the  mill.  All  assays  are  done  by  the  electrolytic  method,  using 
rotating  anodes. 

Most  of  the  flotation  'oil'  is  added  to  the  pulp  at  the  head  of 
the  mill,  being  fed  from  a  tank  by  a  small  bucket-elevator  driven 
by  a  shaft  having  a  cone-step  pulley,  so  that  the  speed  of  the 
elevator  and  the  quantity  of  'oil'  can  be  varied  to  suit  the  tonnage 
of  ore  being  crushed.  This  is  much  more  satisfactory  than  letting 
the  'oil'  drip  from  a  can.  Any  additional  reagent  that  may  be 
required  is  added  at  each  flotation  plant  by  dripping  from  a  can. 

The  following  methods  of  flotation  have  been  tried: 

1.  An  8-compartment  Minerals  Separation  machine  of  standard 
type  (as  described  in  Hoover's  book  on  flotation),  having  a  nominal 
capacity  of  600  tons  per  day.    The  agitation  compartments  are  3  ft. 
square,  and  the  flotation  compartments  or  spitzkasten,  5  by  3  ft.    The 
spindles  are  driven  through  enclosed  bevel-gearing  by  a  pulley  on 
a  horizontal  shaft.     The  overflow  from  the  first  six  compartments 
was  sent  to  the  concentrate-bins  without  'cleaning'  or  further  treat- 
ment designed  to  raise  the  grade  by  eliminating  insoluble  matter 
and  the  overflow  from  the  last  two  compartments  was  returned  to 
the  head  of  the  machine.     This  machine  was  discarded. 

2.  A  12-compartment  Minerals  Separation  machine  of  standard 
type,  of  the  same  capacity  and  driven  in  the  same  manner  as  No.  1, 
the  additional  compartments  being  intended  to  prolong  the  treat- 
ment.    At  first  the  concentrate  and  middling  were  dealt  with  as 
in  No.  1  machine,  but  afterward  the  overflow  from  all  compartments 
was  'cleaned'  in  (3),  next  described. 

3.  An   8-compartment  50-ton   Minerals   Separation   machine   of 
standard  type,  the  spindles  being  driven  by  half-crossed  belts  from 
pulleys  on  a  horizontal  shaft.     The  overflow  from  all  compartments 
was  sent  to  concentrate-bins,  and  the  tailing  was  returned  to  the  head 


FLOTATION  AT  THE  INSPIRATION  MINE,  ARIZONA  87 

of  No.  2  machine.  This  concentrate  contained  about  30%  copper. 
These  two  machines  were  in  use  until  recently. 

4.  An  8-compartment  Minerals  Separation  machine  of  new  type, 
known  as  a  '  sub-aeration  machine/  The  agitation  compartments 
were  covered  on  top,  and  both  mechanical  agitation  and  compressed 
air  were  used.  The  agitation  compartments  contained  cast-iron 
baffle-plates  fixed  to  the  sides,  and  the  impellers  were  different  from 
those  used  in  the  standard  machine,  but  the  spindles  were  driven 
in  the  usual  way.  The  discharge  from  the  agitation  compartments 
to  the  flotation  compartments  was  high  up.  The  air  used  for  the 
aeration  of  the  pulp  was  introduced  through  a  hole  in  the  bottom 
of  each  agitation  compartment  at  a  pressure  of  about  2  Ib.  per  square 
inch.  It  did  not  pass  through  any  porous  medium.  This  machine 
had  the  usual  valves  and  suction-pipes  in  the  bottom,  but  was  after- 
ward altered  to  (5)  a  machine  of  the  Hebbard  type,  with  agitation 
gear  of  the  standard  Minerals  Separation  pattern,  but  with  horizontal 
discs  in  place  of  the  usual  screw-impellers.  Each  spindle  makes 
about  300  r.p.m.  In  the  Hebbard  machine  as  used  in  Australia 
the  agitators  are  driven  from  below.  There  are  no  spitzkasten,  the 
overflow  of  concentrate-froth  taking  place  from  the  agitation  com- 
partments. Consequently  there  are  no  suction-pipes  and  valves  in 
the  bottom,  and  no  plugs  to  draw  and  replace  when  a  stoppage  takes 
place.  The  wooden  partitions  between  the  agitation  compartments 
have  been  removed  and  cast-iron  baffle-plates  about  15  in.  high 
substituted.  Air  is  blown  through  eight  holes  in  the  bottom  as  in 
No.  4  machine  (described  above)  and  water-under  pressure  is  used 
to  prevent  pulp  from  entering  the  air-pipe.  On  a  feed  of  about 
300  tons  per  day  this  machine  has  given  good  results,  and  is  still  in 
use.  The  low-grade  concentrate  made  by  this  machine  is  'cleaned' 
in  another  machine  of  standard  type. 

6.  A  Towne-Flinn  plant,  or  bubble-column  concentrator  with  a 
nominal  capacity  of  50  tons  per  day.  This  consisted  of  (1)  Pachuca 
agitator  in  which  the  pulp  was  mixed  with  oil,  (2)  a  cast-iron 
vertical  cylinder  with  a  bottom  of  carborundum.  The  oiled  pulp  is 
fed  into  the  top  of  the  cylinder  through  a  pipe  that  delivers  it  below 
the  surface.  Air  at  a  pressure  of  5  Ib.  per  square  inch  is  blown 
through  the  carborundum.  Bubbles  are  formed,  that  adhere  to  the 
oiled  sulphide  particles,  forming  a  froth  overflowing  at  the  top  of 
the  cylinder  into  a  launder,  whence  it  flows  to  (3)  a  similar  cylinder 
at  a  lower  level,  where  it  is  'cleaned.'  The  tailing  from  the  first 
cylinder  escapes  through  a  hole  in  the  middle  of  the  carborundum 


88  THE   FLOTATION   PROCESS 

and  flows  through  a  goose-neck  hose  (by  which  the  water-level  in 
the  first  cylinder  is  regulated)  to  (4)  another  cylinder  where  it 
receives  similar  treatment  and  more  concentrate  overflows.  This 
concentrate  also  is  re-treated  in  the  same  cylinder  as  the  concentrate 
from  the  first  cylinder,  and  the  tailing  from  this  cylinder  or  'cleaner' 
is  returned  to  the  Pachuca  agitator  at  the  top  of  the  building  by  a 
centrifugal  pump.  The  air  is  furnished  by  a  Roots  blower.  This 
plant  was  dismantled. 

7.  A  Callow  plant  consisting  of  (1)  Pachuca  agitator  18  ft.  deep 
by  4  in.  diam.,   (2)  five  cells,  each  8J  ft.  long  by  2  ft.  wide,  with 
nominal  capacity  of  50  tons  each  per  day,  (3)  one  cleaner-cell  12  in. 
wide,    (4)    one  air-compressor,    (5)    one   receiver,    (6)    Connersville 
blower  with  a  displacement  of  3.3  cu.  ft.  of  air  per  revolution,  (7)  two 
3-in.  centrifugal  pumps,  (8)  30-hp.  motor. 

Mr.  Callow's  letter  in  the  Mining  and  Scientific  Press  of  May  29 
fully  describes  his  process,  so  I  need  not  go  into  further  particulars, 
except  to  say  that  during  the  past  few  months  the  plant  has  been  run 
without  the  Pachuca  agitators;  but  this  is  by  no  means  advisable. 
This  plant  has  been  running  for  about  nine  months  and  has  given 
better  results  than  any  other  that  has  been  tried  here.  Forty  of 
these  cells  are  being  installed  in  the  new  mill. 

8.  A  machine  invented  by  David  Cole,  of  Morenci,  Arizona,  con- 
sisting of  rectangular  sheet-iron  tanks  with  pipes  laid  horizontally  in 
the  bottom.    The  upper  half  of  these  pipes  is  composed  of  carborun- 
dum, and  air  from  a  blower  is  forced  through  them  with  the  same 
effect  as  in  the  Callow,  Towne-Flinn,  and  other  pneumatic  processes. 
Perforated  wrought-iron  pipes  wrapped  with  flannel  or  canvas  have 
also  been  used.    The  tailing  from  the  first  tank  is  re-treated,  and  the 
concentrate  from  all  tanks  is  re-treated  in  a  'cleaner.'    This  plant  is 
still  running.     A  similar  machine  is  in  use  at  Morenci,  and  one  is 
being  built  at  Cananea,  Sonora. 

9.  The  company's  metallurgist  has  devised  an  apparatus  intended 
to  combine  the  best  points  of  the  other  machines,  but  without  infring- 
ing on  any  patents,  except  those  of  the  Minerals  Separation  American 
Syndicate,  from  whom  the  company  holds  a  license.    It  is  called  the 
Inspiration  machine.    At  first  it  resembled  a  Callow  apparatus  with 
an  almost  flat  bottom,  the  air  being  blown  through  canvas,  but  the 
froth  overflowed  at  one  side  of  the  cell  only,  and  there  were  parti- 
tions which,  however,  did  not  reach  the  bottom.    It  was  twice  as  long 
as  the  ordinary  Callow  cell.     The  first  concentrate  was  re-treated  in 
a  smaller  machine  of  the  same  type,  and  the  tailing  from  this  machine 


FLOTATION  AT  THE  INSPIRATION   MINE,  ARIZONA  89 

was,  as  usual,  returned  to  the  'rougher'  cell.  Recently  other  porous 
media  for  false  bottoms  have  been  tried.  The  machine  is  still  in  the 
experimental  stage. 

It  will  thus  be  seen  that  the  company  has  spared  neither  time  nor 
money  in  endeavoring  to  find  the  best  flotation  process.  The  test-mill 
has  been  working  since  January  1914,  and  about  50  flow-sheets  have 
been  tried.  In  the  laboratory  there  are  6  small  flotation  machines  of 
the  Minerals  Separation  type  in  almost  constant  use. 

The  tailing  from  all  the  flotation  plants  is  run  over  tables,  those  in 
use  being  Wilfley,  Deister  Machine  Co.'s  double-deck  simplex  sand 
concentrator,  Deister  Machine  Co.'s  four-deck  table,  Deister  slime 
table,  and  Deister  Concentrator  Co.'s  double-deck  table.  At  one  time 
the  ore  was  concentrated  on  tables  before  going  through  the  flotation 
process,  but  this  was  not  found  suitable  for  the  Minerals  Separation 
process,  as  it  left  too  little  mineral  in  the  ore,  and  for  this  and  other 
reasons  it  was  discarded.  The  mineral  saved  on  the  tables  is  mostly 
pyrite.  The  234  tables  in  the  new  mill  are  Deister  Machine  Co.'s 
double-deck  type,  the  same  as  used  in  the  Miami  Copper  Co.'s  mill. 
No  tests  were  made  with  any  kind  of  vanner.  The  sand  and  slime 
were  run  over  the  same  tables  without  classification,  but  this  will  be 
altered  in  the  new  mill. 

The  tailing  from  the  tables  flows  to  the  dam,  the  retaining-wall 
being  built  by  allowing  the  coarse  sand  to  escape  through  cones  or 
inverted  pyramids  attached  to  the  tailing-launder. 

The  concentrate  from  all  flotation  plants  and  the  tables,  contain- 
ing about  28%  copper,  16%  iron,  and  26%  insoluble  matter,  goes  to 
a  drag-classifier.  From  there  the  coarse  concentrate  goes  direct  to  an 
Oliver  filter  and  the  fine  to  a  V-shaped  settling-tank,  thence  to  the 
filter.  The  concentrate,  after  filtering,  still  contains  a  good  deal  of 
moisture.  It  is  trammed  to  a  bin  adjoining  a  branch  of  the  standard- 
gauge  railway  and  loaded  into  bottom-discharge  steel  cars  belonging 
to  the  International  Smelting  Co.  Formerly  it  was  sent  to  El  Paso, 
Texas. 

Water  for  the  mill  and  domestic  purposes  is  obtained  by  pumping 
from  wells  in  the  flat  country  about  three  miles  distant.  A  large 
concrete  reservoir  has  been  built  on  a  hill  near  the  mill.  Electric 
power  is  obtained  from  the  power-house  at  the  Roosevelt  dam  about 
40  miles  distant,  belonging  to  the  U.  S.  Reclamation  Service,  and  the 
service  is  fairly  satisfactory.  The  Inspiration  company  has  an  in- 
terest in  the  power-house  at  the  International  smelter  near-by,  where, 
in  case  of  emergency,  a  supply  of  electricity  can  be  generated  by 


90 


THE  FLOTATION   PROCESS 


steam  from  waste  heat  from  the  reverberatories  and  from  oil-fired 
Stirling  boilers. 

As  mentioned  in  the  annual  report  of  the  company  (a  summary  of 


FlG.    16.      FLOW-SHEET    OF    THE    INSPIBATION    MILL.       THE    BOASTING    FUBNACE    FOB 
CONCENTBATE   IS    AT    THE    SMELTEB   NEAB-BY. 

which  appeared  in  the  Mining  and  Scientific  Press  of  May  1,  1915), 
172,722  tons  of  ore  was  treated  in  this  mill  in  1914,  so,  although  only 
a  test  mill,  it  handles  a  fairly  large  tonnage.  During  the  month  of 
February  1915,  90.3%  of  the  copper  occurring  in  the  form  of  sul- 
phides was  recovered.  The  mill  has  been  visited  by  mining  men  from 
all  parts  of  the  world. 


FLOTATION  IN  A  MEXICAN   MILL  91 

FLOTATION   IN   A   MEXICAN   MILL 

By  A  SPECIAL  CORRESPONDENT 
(From  the  Mining  and  Scientific  Press  of  July  24,  1915) 

PRESENT  CONCENTRATING  METHODS.  The  mill  receives  200  tons 
per  day  of  crude  mine  ore.  After  being  crushed  to  2-inch  size,  this 
ore  is  passed  over  a  picking-belt,  where  one  ton  of  high-grade  ore  and 
four  tons  of  waste  are  removed  each  day.  The  remaining  195  tons  of 
second-class  ore  is  crushed  in  stamp-batteries,  to  pass  a  4-mesh  screen. 
Lime-water,  in  the  proportion  of  7  of  water  to  1  of  ore,  is  added  in 
the  battery.  The  pulp  from  these  is  classified  roughly,  the  coarse  sand 
being  ground  in  a  Hardinge  mill  to  pass  a  20-mesh  screen.  The  pulp 
is  again  classified  roughly  into  four  sizes  of  sand  and  one  size  of  slime. 
The  sand  is  concentrated  on  Wilfley  tables  and  the  slime  (after  being 
settled  to  7 : 1  in  cone-bottom  tanks)  is  concentrated  on  Deister  tables. 

The  slime-tailing,  from  the  Deister  tables,  is  re-concentrated  on 
vanners.  The  tailing  from  the  vanners  settles  to  3J  tons  of  water  per 
ton  of  slime ;  the  water  being  further  reduced  to  J :  1  in  a  vacuum- 
filter.  The  filter-cake  is  washed  with  weak  barren  solution  before 
being  sent  to  the  cyanide  plant. 

The  sand-tailing  from  the  Wilfley  tables  of  the  stamp-mill  is 
classified  carefully  in  mechanical  classifiers ;  the  slime  under-size  joins 
the  slime-tailing  from  the  re-concentrating  vanners,  and  the  sand 
(after  the  addition  of  cyanide  solution)  enters  the  tube-mill  circuit, 
where  it  is  joined  by  50  tons  per  day  of  dump-tailing.  All  tube- 
milling  is  done  in  cyanide  solution.  After  passing  through  the  tube- 
mills,  the  combined  current  and  dump  sands  are  re-concentrated  on 
Wilfley  tables.  The  tailing  from  these  tables  is  classified,  the  coarse 
sand  re-entering  the  tube-mill  circuit  and  the  slimed  sand  being  thick- 
ened in  three  24-ft.  Dorr  vats  before  entering  the  cyanide  plant. 

METALLURGICAL  RESULTS  OF  PRESENT  METHODS 

Gold,  Silver,  Copper,  Lead. 

oz.  oz.  %  % 

The  feed  to  the  stamp-mill  assays 0.1  35.4  0.25  0.7 

The  concentrate  assays  2.0  570.0  2.0  10.0 

The  tailing,  after  concentration,  assays  ...  0.03  18.0  0.15  0.4 

The  recovery  therefore  is:  gold,  65;  silver,  48;  copper,  35;  and 
lead,  45%. 

NECESSITY  FOR  BETTER  CONCENTRATION.  The  above  data  show  that 
a  little  more  than  half  the  gold  is  being  recovered  in  concentration, 


92  THE   FLOTATION    PROCESS 

and  that  the  recovery  on  silver,  lead,  and  copper  is  less  than  half  the 
contents  in  the  original  ore. 

Tests  indicate  that  more  than  90%  of  the  metal  in  the  original  ore 
occurs  in  the  form  of  sulphides.  Hence  half  of  the  metallic  sulphides 
of  the  original  ore  enters  the  cyanide  plant.-  This  is  undesirable  for 
the  following  reasons : 

1.  The  extraction  of  silver  from  sulphide  metals  is  poor  in  the 
cyanide  plant ;  the  concentrate  produced  from  panning  current  residue 
assays  between  50  and  100  oz.  silver  per  ton,  and  the  tailing  from  pan- 
ning invariably  assays  below  2  oz.,  even  when  the  residue  assays  as 
high  as  5  oz. ;  showing  that  the  poor  extraction  is  due  to  undissolved 
silver  in  the  sulphides. 

2.  The  presence  of  metallic  sulphides  increases  the  cyanide  con- 
sumption.   The  chemical  consumption  of  cyanide  is  reduced  from  4  to 
1  Ib.  per  ton  when  the  metallic  sulphides  are  removed  from  the  head- 
ing to  the  cyanide  plant.    The  present  excessive  cyanide  consumption 
is  due  almost  entirely  to  the  solution  of  copper  from  the  ore. 

3.  The  presence  of  copper  and  zinc  sulphides  in  the  cyanide  pulp 
fouls  the  solution,  thus  decreasing  the  extraction  from  the  rest  of 
the  ore. 

The  possibility  of  improving  results  by  better  concentration  of  the 
ore  has  long  been  recognized.  For  this  reason,  arrangements  were 
made  for  re-concentrating.  Both  arrangements  have  effected  a  re- 
duction of  assay-value  in  the  final  residue  and  a  corresponding  in- 
crease of  profit. 

METHODS  FOR  IMPROVING  PRESENT  CONCENTRATION.  Lately,  exten- 
sive tests  have  been  made  to  determine  the  possibility  of  still  closer 
concentration.  Careful  panning  reduces  the  average  feed  to  the  cya- 
nide plant  from  18  oz.  silver  to  10  oz.  per  ton. 

Canvas  tables  give  slightly  poorer  results.  A  full-sized  canvas 
table,  treating  tailing  from  the  Deister  tables  (assaying  20  oz.  per 
ton)  produced  15  oz.  tailing — an  extraction  of  25%.  Further  tests 
along  this  line  were  discontinued  on  account  of  securing  much  better 
results  from  laboratory  flotation  tests. 

LABORATORY  FLOTATION  TESTS.  All  flotation  tests,  made  in  the 
laboratory,  were  run  in  separatory  funnels.  The  general  procedure  in 
the  tests  was  to  mix  100  grams  of  minus  200-mesh  ore  with  water  in 
proportion  of  four  of  water  to  one  of  ore.  Suitable  amounts  of  oil 
were  then  added  and  the  mixture  shaken  violently.  After  allowing 
the  pulp  to  settle  for  a  few  moments,  the  bottom  cock  of  the  funnel 
was  opened  and  the  tailing  run  into  a  second  separatory  funnel  for 


FLOTATION  IN  A  MEXICAN   MILL  93 

another  flotation  treatment;  the  cock  being  closed  before  the  froth 
began  to  run  out.  This  process  was  repeated,  on  the  tailing,  from  five 
to  seven  times.  Several  hundred  tests  have  been  run,  all  possible 
variations  of  conditions  being  tried.  The  results  of  the  tests  led  to 
the  following  conclusions : 

1.  All  ores  from  the  mine  may  be  treated  by  flotation.     Semi- 
oxidized  ore  from  one  level  yields  a  tailing  assaying  10  oz.  silver  per 
ton,  while  the  oxidized  ore  from  another  level  gives  a  tailing  contain- 
ing only  2  oz.  per  ton.    The  tailing  from  average  ore,  when  conditions 
for  flotation  are  right,  is  4.5  oz.  silver  per  ton. 

2.  The  grade  of  tailing  appears  to  be  independent  of  whether  the 
original  ore  is  treated  by  flotation,  or  whether  wet  concentration  pre- 
cedes flotation. 

3.  The  alkalinity  during  flotation  must  be  between  0.01  and  0.05 
Ib.  per  ton  of  solution.     The  best  results  are  secured  when  the  alka- 
linity is  0.025  Ib.    When  the  alkalinity  is  too  low,  the  extraction  is 
poor  although  the  concentrate  is  clean.     When  the  alkalinity  is  too 
high,  both  the  extraction  and  grade  of  concentrate  are  poor.    When 
the  alkalinity  is  right  (0.025  Ib.)  both  the  extraction  and  grade  of 
concentrate  are  best.     The  maintenance  of  proper  alkalinity  will  re- 
quire the  most  care  of  anything  in  the  plant ;  although  it  will  not  be 
more  difficult  than  the  maintenance  of  proper  cyanide  strength  in  the 
cyanide  plant. 

4.  The  dilution  may  range  between  3£ :  1  and  7:1;  with  the  best 
results,  on  average  ore,  between  4 : 1  and  6:1.     When  the  pulp  is 
sandy  a  low  dilution  is  best:  pure  sand,  ground  to  200-mesh,  requires 
a  dilution  of  1:1.    Average  slime,  like  the  Deister  feed,  on  the  other 
hand,  requires  a  dilution  of  8 : 1.    Good  extraction  may  be  secured  on 
either  sand  or  slime,  provided  approximately  the  proper  dilutions  are 
secured  in  each  case.    Proper  dilutions  will  be  easy  to  maintain  in  the 
plant,  for  the  range  for  the  best  work  is  comparatively  large;  and 
when  either  an  excess  of  sand  or  an  excess  of  slime  occurs  in  the  ore, 
the  proper  dilution  will  automatically  adjust  itself;  for  the  sand  of 
itself  will  settle  to  a  thick  pulp,  while  the  slime  will  not  settle  well, 
but  will  remain  thin. 

5.  The  temperature  is  not  a  matter  of  vital  interest.     The  ex- 
traction is  slightly  better  and  the  grade  of  concentrate  considerably 
higher  when  the  temperature  is  over  100 °F.,  but  good  results  have 
been  secured  with  the  temperature  as  low  as  40 °F.     It  will  not  be 
necessary  to  arrange  for  heating  the  pulp,  especially  at  the  start. 

6.  Fine  grinding  is  necessary  for  good  results  in  flotation.    When 


94  THE  FLOTATION   PROCESS 

the  mill-heading  was  crushed  to  60-mesh,  the  tailing  from  flotation 
assayed  0.08  oz.  gold,  and  11  oz.  silver ;  when  the  same  ore  was  crushed 
to  100-mesh,  the  tailing  assayed  0.04  oz.  gold  and  5  oz.  silver;  and 
when  the  crushing  was  carried  to  200-mesh,  the  tailing  assayed  0.02 
oz.  gold  and  3.75  oz.  silver. 

[The  question  of  the  kind  of  crushing  mechanism  best  adapted  to 
preparing  ore  for  notation  is  vital ;  at  present  the  tube-mill,  ball-mill, 
and  disc-crusher  hold  the  field. — EDITOR.] 

7.  The  best  flotation  agents,  so  far  tested,  are  pine-oils.     Low- 
grade  pine-oil  gave  as  good  results  as  the  higher-grade  varieties. 
S.  S.  pine-oil,  of  the  General  Naval  Stores  Co.   (cost  26c.  per  gal., 
f.o.b.  factory)   has  given  exceptionally  good  results.     For  the  best 
work  in  flotation  it  is  necessary  to  have  this  oil  present  to  the  extent 
of  0.6  Ib.  per  ton  of  ore.    In  actual  plant-practice,  where  the  water 
is  returned  again  and  again  to  the  top  of  the  mill,  the  consumption 
of  oil  will  probably  be  about  J  Ib.  per  ton  of  ore.    This  oil  will  cost, 
delivered,  8c.  per  pound. 

Pine-tar  oil  is  much  cheaper.  It  gives  good  extraction,  but  the 
grade  of  concentrate  is  low.  Cresylic  acid,  when  used  with  pine-oils, 
increases  the  extraction  about  J  oz.  silver  per  ton.  This  hardly  pays 
for  its  use. 

8.  In  the  laboratory  tests  the   grade  of  concentrate  was  low, 
averaging  200  oz.  silver  per  ton.     This  concentrate  could  be  raised 
to  1100  oz.  by  re-treating  the  concentrate  by  flotation. 

9.  Cyanide  tests,  run  on  tailing  from  the  flotation  tests,  produced 
residues  assaying  less  than  1   oz.   silver  per  ton,   with   a  cyanide 
consumption  of  less  than  1  Ib.  per  ton. 

10.  The    dump-tailing   cannot   be    easily   treated   by   flotation. 
When  the  methods  of  flotation  that  are  applicable  to  mine  ore  are 
applied  to  the  pump-tailing,  the  results  are  nil.    Furthermore,  when 
the  water  that  has  been  in  contact  with  the  pump-tailing  is  used 
for  diluting  mine-ore,  the  mine-ore  cannot  be  treated  advantageously 
by  flotation.    Experiments  show  that  both  these  effects  are  due  to  the 
presence    of    soluble    sulphates    (chiefly    those    of    magnesium    and 
calcium)   in  the  pump-tailing.     The  injurious  effect  of  magnesium 
sulphate  can  be  overcome  largely  by  an  excess  of  oil.     No  method 
of  overcoming  the  injurious  effects  of  calcium  sulphate  has  yet  been 
discovered  in  the  tests. 

When  the  dump-tailing  is  washed  in  fresh  water  half  a  dozen 
times,  before  being  treated  by  flotation,  the  results  of  flotation  are 
as  satisfactory  as  is  the  case  with  mine-ore.  However,  a  plant  for 


FLOTATION  IN  A  MEXICAN   MILL  95 

washing  the  dump -tailing  would  be  more  expensive  than  the  small 
tonnage  of  this  material  warrants,  and  the  operation  of  such  a  plant 
would  necessitate  the  waste  of  more  water  than  is  available.  Some 
other  method  of  rendering  the  dump-tailing  susceptible  to  flotation 
may  be  devised ;  but  the  small  tonnage  does  not  warrant  any  extended 
investigation.  The  best  thing  to  do,  especially  at  the  start,  is  to 
send  the  dump-tailing  direct  to  the  cyanide  plant  (after  concen* 
trating  the  ground  sand  on  Wilfleys)  as  at  present. 

11.  As  a  result  of  the  laboratory  experiment,  it  was  decided 
that  full-sized  tests  should  be  conducted  in  the  plant  on  run-of- 
mine  ore. 

PLANT  TESTS.  For  this  purpose,  there  were  set  aside  for  the 
flotation  circuit:  one  battery  of  five  stamps,  two  "Wilfley  tables, 
one  classifier,  one  tube-mill,  one  24-ft.  settler,  and  one  pump  for 
returning  the  water  from  the  settling-tank  to  the  head  of  the  mill. 

A  flotation-cell  of  the  pneumatic  type  was  first  tried.  When 
treating  20-oz.  heading  this  machine  produced  a  290-oz.  concentrate 
and  a  15.3-oz.  tailing.  This  was  far  from  satisfactory. 

Another  machine  consisted  of  a  series  of  mechanical-agitation 
chambers,  alternating  with  a  series  of  settling-chambers.  From  the 
start,  this  machine  has  given  excellent  results.  In  spite  of  many 
mechanical  difficulties,  and  trouble  with  inexperienced  operators,  the 
tailing  from  the  plant  has  averaged  but  little  above  5  oz.  silver 
per  ton,  and  the  concentrate  has  averaged  above  600  oz.,  without 
re-concentration. 

The  chief  weaknesses  of  mechanical  agitation,  as  ascertained  in 
this  mill,  are  as  follows : 

1.  The  complex  system  of  shafts  and  counter-shaft,  with  the 
corresponding  drives,  bearings,  etc. 

2.  The    difficulty   of   adjustment;    any   slight   change    in   feed 
necessitating  a  change  in  the  valves  of  each  chamber. 

3.  The   difficulty  of  the  passages  between  chambers  becoming 
clogged. 

SUBMERGED  AGITATION.  It  has  been  attempted  to  evolve  a  flotation 
machine  to  overcome  these  weaknesses,  and  at  the  same  time  give 
results  as  good  as  the  mechanical  agitation  plant.  A  small  machine 
(capacity  3  tons  per  day)  has  been  constructed,  and  this,  after 
many  alterations,  has  yielded  a  3.7-oz.  tailing  and  a  680-oz.  concen- 
trate, when  treating  10-oz.  feed.  This  machine  employs  a  somewhat 
novel  principle  of  flotation — that  of  submerged  agitation — the 
mixture  of  pulp,  oil,  and  air  being  violently  agitated  in  a  partly 


96  THE   FLOTATION   PROCESS 

closed  chamber,  under  the  hydrostatic  pressure  of  several  feet  of 
pulp  in  the  settling-chambers  above. 

In  construction,  this  machine  is  simpler  than  the  machine  using 
mechanical  agitation.  It  consists  essentially  of  a  V-shaped  box  or 
trough,  divided  into  compartments  by  a  series  of  vertical  partitions. 
At  the  bottom  of  each  partition  is  an  agitation-chamber.  Agitation 
is  supplied  by  a  paddle-wheel  in  each  chamber.  All  the  paddle- 
wheels  are  mounted  upon  a  single  horizontal  shafting,  which  passes 
the  entire  length  of  the  trough,  leaving  the  end  partitions  through 
stuffing-boxes.  The  pulp  enters  each  agitation-chamber  through  an 
opening  around  the  shafting,  and  leaves  the  agitation-chamber 
through  an  adjustable  aperture,  at  a  slight  distance  from  the  shafting. 
The  agitator  thus  acts  slightly  as  a  centrifugal  pump,  overcoming  the 
friction  loss  in  the  passage  from  one  compartment  to  another,  and 
keeping  the  height  of  the  pulp  the  same  in  all  the  settling-chambers. 
The  adjustment  of  the  aperture  is  arranged  to  increase  or  decrease 
the  centrifugal  force.  This  adjustment  occasions  much  less  difficulty 
than  is  experienced  in  mechanical  agitation,  where  the  flow  from 
one  compartment  to  another  is  merely  throttled. 

Also,  in  the  new  plant  there  are  no  pipes  to  become  clogged, 
the  passage  of  pulp  from  one  cell  to  another  being  along  a  rapidly 
revolving  shafting,  which  keeps  all  material  in  suspension.  The 
concentrate  overflows  from  both  edges  of  the  trough,  thus  being 
removed  more  promptly  than  in  a  plant  using  mechanical  agitation. 

Further  tests  with  the  small  machine  are  being  made,  and  a 
larger  machine  (capacity  40  tons  per  day)  is  being  constructed,  for 
thoroughly  testing  the  principles  involved.  The  40-ton  machine  will 
be  constructed  with  the  idea  of  using  it  for  re-concentration  of  the 
concentrate,  should  a  full-sized  flotation  plant  be  installed. 

SIMPLE  MECHANICAL  AGITATION.  The  machine  has  now  been 
operating  intermittently  for  a  month.  During  that  month  it  ran  six 
days  continuously,  treating  25  tons  of  29-oz.  pulp  and  producing 
6.4-oz.  tailing  and  600-oz.  concentrate.  During  the  first  five  days 
of  the  following  month,  careful  tests  were  run  to  compare  flotation 
results  with  those  from  current  concentrating  practice.  The 
following  tables  give  the  summary  of  results  from  these  tests. 

MILL-TESTS.  Flotation  v.  Present  Concentration  Practice.  Flota- 
tion plant  takes  25  tons  per  day  of  mill  heading  after  being  crushed 
to  20-mesh  by  stamps,  concentrated  on  Wilfleys,  and  passed  through 
a  tube-mill. 


FLOTATION   IN  A  MEXICAN   MILL  97 

METALLURGICAL  RESULTS,  PER  TON  OF  ORIGINAL  ORE,  USING  FLOTATION 

, Assay ^  , —  Contents  — N 

Tons.            Gold.           Silver.  Gold.          Silver. 

Mill-heading    1.0000            0.125            39.81  0.125            29.81 

Wilfley  concentrate 0.0313             3.070           663.27  0.096            20.76 

Wilfley  tailing   0.9684             0.030            19.70  0.029            19.05 

Flotation  concentrate 0.0207            1.190           692.78  0.025            14.34 

Flotation  tailing .0.9477            0.004              4.98  0.004              4.71 

Cyanide  residue 0.001              1.00  0.001              0.95 

Cyanide  bullion   .  0.003              3.76 


LIQUIDATIONS* 

Wilfley  and  flotation  concentrate,  tons 0.52 

Gold,  0.121  oz.  at  $20 $2.42 

Silver,  35.10  oz.,  95%  =  33.345  oz.  at  50c 16.67 

Copper,  3%  -0.3  =  2.7%;  2.81  Ib.  at  8.2c 0.23 

Lead,  11.8%-  1.5  =  10.3%;  90%  at  3c 0.29 

$19.61 

Less  haulage,  freight,  and  treatment,  at  $19.67  per  ton $1.02 

Less  taxes,  commissions,  etc.,  7.44% 1.45       2.47 


Bankable  funds  from  concentrate  per  ton  of  ore $17.14 

Bullion  from  flotation-tailing,  per  ton  of  ore,  5.56  oz.  gross: 

Gold,  0.003  oz.  at  $20.67 $0.06 

Silver,  3.76  oz.  at  50c .   1.88 


$1.94 

Less  haulage,  treatment,  l.OSc.  per  oz $0.06 

Less  express,  duties,  etc.,  7.8% 0.15      0.21 


Bankable  funds  from  bullion  per  ton  of  ore $1.73 

*Throughout  this  article  values  are  given  in  U.  S.  Currency. 
PRODUCTS  PER  TON  OF  ORIGINAL  ORE 

Assay.  Insol- 

Tons.       Gold.        Silver.    Copper.     Lead.     Zinc.      uble. 
Oz.  Oz.          %  %  %  % 

Wilfley  concentrate.... 0.0313  3.07  663.27  2.75  12.00  12.7  24.5 
Flotation  concentrate.. 0.0207  1.19  292.78  3.36  11.55  13.9  34.3 
Average  concentrate.  .0.0520  2.327  675.00  3.00  11.80  13.2  28.4 

Bullion    . 0.003  3.76         

PRESENT  PRACTICE.  During  the  five  days  the  flotation  test  was 
being  run,  the  rest  of  the  mill  received  160  tons  per  day  of  the 
same  grade  of  mill-heading.  This  was  treated  on  Wilfley  and  Deister 
tables  and  the  tailing  re-concentrated  on  Wilfleys  and  vanners. 


98 


THE  FLOTATION   PROCESS 


METALLURGICAL  RESULTS,  PER  TON  .OF  ORIGINAL  ORE 

, Assay N  /• —  Contents  — N 

Tons.             Gold.          Silver.  Gold.  Silver. 

Mill-heading    1.00000            0.125            39.81  0.1250  39.81 

Stamp-mill  concentrate. .  .0.03650            1.930          518.00  0.0706  18.94 

Wilfley   re-concentrate 0.00375            1.760           286.44  0.0066  1.08 

Vanner  re-concentrate 0.00060            0.780          370.92  0.0005  0.22 

Tailing    0.95815            0.050            20.40  0.0473  19.57 

Residue   0.95815            0.0048            3.12  0.0046  2.98 

Bullion 0.0427  16.59 

Bullion,  24.88  oz.  gross;  gold,  0.0427  oz.;  silver,  16.59  oz.  per  ton. 

LIQUIDATION,  PER  TON  OF  ORIGINAL  ORE 

Concentrate,  tons 0.04085 

Gold,  0.0777  oz.  at  $20 $1.55 

Silver,  20.24  oz.;  95%  at  50c 9.61 

Copper,  2.41%- 0.3  =  2.11%;  1.73  Ib.  at  8.2c 0.14 

Lead,  9.7%- 1.5  =  8.2%;  90%  at  3c 0.18 

$11.48 

Less  haulage,  freight,  and  treatment,  at  $19.67  per  ton $0.80 

Less  taxes,  commission,  and  expense,  7.44% 0.86      1.66 

Bankable  funds  per  ton  of  ore $9.82 

Bullion  from  current  tailing,  24.88  oz.  gross: 

Gold,  0.0427  oz.  at  $20.67 , . . .  $0.88 

Silver,  16.59  oz.  at  50c 8.29 

$9.17 

Less  haulage  and  treatment,  at  1.08c.  per  oz $0.26 

Less  express,  taxes,  etc.,  7.8% 0.72       0.98 

Bankable  funds  per  ton  of  ore $8.19 


PRODUCTS  PER  TON  OF  ORIGINAL  ORE 


Tons. 

Stamp-mill  concentrate. .  0.03650 
Wilfley  re-concentrate . . .  0.00375 
Vanner  re-concentrate. . .  0.00060 
Total  concentrates..  ..0.04985 


Gold. 
Oz. 
1.93 
1.76 

0.78 
1.90 


Assay. 

Silver.  Copper.  Lead. 
Oz.          %  % 

2.56       10.40 
1.03         3.37 


518.00 
286.44 
370.92 
496.00 


1.00 
2.41 


5.86 
9.7 


Zinc. 
% 

12.9 
6.0 
4.7 

12.15 


Insol- 
uble. 

% 

24.50 
45.28 
56.22 
27.00 


COSTS.  Labor  and  repair  costs  will  remain  about  the  same  as 
now.  Two  high-class  operators  in  the  present  re-treatment  plant 
will  be  replaced  by  three  cheap  operators  in  the  flotation  plant. 

Power  consumption  will  be  increased  about  40  hp.  This  will 
cost  5c.  per  ton. 


FLOTATION  IN  A  MEXICAN   MILL  99 

Oil  consumption  will  be  about  J  Ib.  per  ton  of  ore.  J  Ib.  @  8c.  =  2c. 
per  ton. 

The  total  increase  in  the  cost  of  concentration  will  therefore  be 
about  7c.  per  ton. 

The  present  cyanide  consumption  per  ton  of  ore  is  6  Ib.,  of  which 

2  Ib.   is  mechanically  lost.     Small  laboratory  tests  show  that  the 
chemical  consumption  of  cyanide  when  flotation-tailing  is  treated, 
is  only  1  Ib.  per  ton  of  ore.     This  is  3  Ib.  less  than  the  consump- 
tion when  current  tailing  is  treated.     If  this  result  is  sustained  in 
actual  plant-practice,  the  saving  in  cyanide  alone  will  amount  to 

3  x  19c.  =  57c.  per  ton  of  ore. 

The  present  cost  of  precipitation  and  melting  is  2.56c.  per  fine 
ounce. 

In  present  practice  16.6  fine  ounces  are  produced  per  ton  of  ore. 
When  flotation  tailing  is  treated,  only  3.7  oz.  are  produced  per  ton 
of  ore.  This  means  an  excess  of  12.9  oz.  produced  in  present  practice : 
129  X  2.56c.  =  33c.  per  ton  of  ore. 

FINANCIAL  STATEMENT 

Flotation  v.  Present  Practice,  Per  Ton  of  Original  Ore. 

Present 

practice.  Flotation. 

Bankable  funds;  marketing  concentrate $9.82  $17.14 

Bankable  funds;  marketing  bullion 8.19  1.73 

Increased  cost  of  concentration 0.07  .... 

Decreased  cost  of  cyanide 0.57 

Decreased  cost  of  melting  and  precipitation 0.28 


$18.08  $19.72 

Increased  profit  per  ton  from  notation,  200  tons  per  day  at  $1.64  =  $328 
increased  profit  per  day  or  $9840  increased  profit  per  month. 

The  above  is  calculated  on  the  basis  of  results  from  a  single  mill- 
test  of  5  days'  duration.  During  this  interval  the  heading  to  the 
mill  and  the  residues  were  excessively  high;  indicating  a  greater 
advantage  in  favor  of  the  flotation  plant  than  is  actually  warranted. 

The  estimate  of  probable  profit  may  be  revised  roughly  by  using 
the  metallurgical  results  of  the  past  two  months  for  the  basis  of 
calculations.  During  two  months  the  heading  to  the  cyanide  plant 
has  averaged  17.8  oz.  silver,  and  the  residue  has  averaged  2.75  oz. 
per  ton.  The  residue  from  cyanide-flotation  tailing  would  assay 
1  oz.  per  ton.  This  indicates  an  increased  extraction  of  1.75  oz. 
silver  per  ton  of  ore.  1.75  oz.  at  41c.  =  72c.  increased  profit  per  ton. 

The  indicated  decrease  in  cyanide  consumption    (as  determined 


100  THE  FLOTATION   PROCESS 

solely  in  the  laboratory)  is  3  Ib.  per  ton  of  ore.     Reducing  this  to 
2J  X  19c.  =  47c.  per  ton  of  ore. 

The  decreased  cost  of  precipitation  and  melting  may  be  figured 
as  follows : :  Cost  of  precipitation  and  melting,  per  fine  ounce,  has 
been  2.4c.  The  decreased  production  of  bullion,  due  to  notation, 
would  be  11  oz.  per  ton  of  ore.  11  oz.  at  2.4c.  =  26.4c.  When  fixed 
charges  are  considered,  this  should  be  reduced  to  20c.  per  ton. 

When  the  profit  from  marketing  an  increased  amount  of  lead 
and  copper  is  balanced  against  the  increased  loss  occasioned  by 
marketing  the  silver  and  gold  as  concentrate  instead  of  bullion, 
there  is  a  deficit  of  17c.  per  ton  of  ore. 

The  matter  may  be  summarized  as  follows: 

Per  ton. 

Increased  extraction $0.72 

Decreased  cyanide  consumption 0.47 

Decreased  cost  of  precipitation  and  melting 0.20 


$1.39 
Increased  cost  of  marketing 0.17 


Profits  per  ton  of  ore $1.22 

The  average  tonnage  of  mine-ore  for  the  past  two  months  has 
been  5761  tons.  Hence  the  indicated  increase  in  monthly  profit 
would  be  5761  X  $1.22  =  $7028.42. 

INSTALLATION  OP  FLOTATION  PLANT.  Should  a  flotation  plant  be 
installed,  operations  in  the  stamp-mill  will  continue  as  at  present; 
though  it  may  be  deemed  advisable,  after  the  flotation  plant  is 
running  smoothly,  to  eliminate  concentration  in  the  stamp-mill,  and 
depend  upon  the  flotation  plant  for  all  concentration. 

Re-concentration  of  current  tailing  on  vanners  and  Wilfleys  will 
be  discontinued  from  the  start. 

The  dump-tailing  will  be  treated  as  at  present,  with  the  exception 
that  this  material  will  enter  the  plant  only  in  the  day-time.  One 
tube-mill,  one  classifier,  one  elevator,  and  the  re-concentrating  Wilfley 
tables  will  be  kept  separate  from  this  circuit,  which  will  be  in 
cyanide  solution.  All  lime  for  the  cyanide  plant  will  enter  this 
circuit.  One  of  the  24-ft.  tanks  and  one  of  the  pumps  must  be 
reserved  for  the  dump-tailing  circuit. 

All  the  tube-milling  of  current  sand  tailing  will  be  done  in 
mill-water,  instead  of  cyanide  solution. 

The  ground  sand,  together  with  the  current  slime,  will  be  settled 
in  two  of  the  24-ft.  thickening-tanks,  and  will  then  enter  the  flotation 


FLOTATION   IN  A  MEXICAN   MILL  101 

plant.  From  the  flotation  plant,  the  tailing  will  flow  to  the  two 
33-ft.  thickening-tanks.  The  thickened  pulp  from  these  tanks  will 
be  de-watered  and  washed  in  the  vacuum-filter  before  entering  the 
cyanide  plant.  * 

All  lime  for  the  mill-circuit  will  be  added  as  an  emulsion  to  the 
flotation-tailing  launder,  where  it  will  be  under  direct  control  of 
the  flotation-operator.  The  water  in  the  23-ft.  thickening-tanks  will 
contain  about  0.4  Ib.  dissolved  lime  per  ton.  This  is  ample  for  good 
settling.  The  overflow  from  these  tanks  will  be  reduced,  by 
consumption,  to  about  0.1  Ib.  per  ton.  This  is  sufficient  for  fair 
settling  in  the  cone-bottom  tanks  of  the  stamp-mill.  By  the  time  the 
pulp  reaches  the  24-ft.  thickening-tanks  the  lime  will  be  reduced 
to  0.03  Ib.  per  ton.  This  low  lime  will  be  extremely  detrimental  to 
good  settling  in  these  tanks. 

INSTALLATION  REQUIRED.  The  matter  of  supplying  proper  settling 
and  de-watering  facilities  will  be  the  most  serious  and  most  expensive 
part  of  the  installation. 

The  two  24-ft.  thickening-tanks,  to  be  used  in  the  flotation-circuit, 
must  be  triple-decked.  It  will  also  probably  be  found  necessary  to 
double-deck  the  32-ft.  steel  thickening-tank.  The  work  on  settling- 
tanks  will  cost  about  $6000. 

By  increasing  the  settling  capacity,  the  pulp  will  probably  be 
settled  to  a  sufficient  thickness  so  that  the  vacuum-filter  will  be  able  to 
handle  the  combined  sand-slime  feed. 

It  may  be  found  necessary,  however,  to  add  another  unit  to  this 
plant. .  This  will  cost  $2000. 

The  flotation  plant  will  consist  of  two  units  (each  .of  which  will 
be  able  to  treat  the  total  tonnage  of  current  tailing)  and  one  smaller 
clean-up  machine.  The  whole  plant  will  cost  about  $3000.  A  filter- 
press  for  handling  the  concentrate  will  cost  $2000.  Tanks,  air-lifts, 
launders,  and  buildings  will  cost  $2000.  Thus  the  whole  installation 
will  cost  $15,000,  or  $20,000  at  the  most.  The  addition  of  the 
flotation  plant,  for  treating  current  tailing,  will  increase  the  profit 
about  $7000  per  month.  Practically  all  ore  from  the  mine  may  be 
treated  by  flotation. 


102  THE  FLOTATION  PROCESS 


FROTH   AND   FLOTATION 

(From  the  Mining  and  Scientific  Press  of  July  31,  1915) 

In  the  issue  for  November  1903  of  the  California  Journal  of 
Technology  there  appeared  an  article  describing  the  experimental 
work  done  on  oil-flotation  by  three  senior  students  in  the  University 
of  California.  The  article  is  entitled  'Experiments  on  the  Elmore 
Process  of  Oil  Concentration'  by  W.  F.  Copeland,  Drury  Butler,  and 
Jas.  H.  Wise. 

At  the  outset  they  state : 

1  'The  process  depends  upon  the  fact  that  minerals  with  a  metallic 
lustre,  when  treated  in  the  form  of  a  wetted  pulp,  adhere  to  oil,  while 
earthy  minerals  do  not.  Two  distinct  operations  are  involved;  first, 
the  separation  of  the  metallic  mineral  from  the  gangue  by  means  of 
oil;  second,  the  extraction  of  the  mineral  from  the  oil. 

"The  ideas  underlying  the  first  operation  were  patented  by  John 
Turnbridge  of  Newark,  N.  J.,  in  1878.  In  1886  Carrie  J.  Everson, 
of  Chicago,  contributed  the  idea  that  the  concentration  was  aided  by 
the  presence  of  an  acid  solution,  and  patented  the  same.  But  the 
absence  of  a  successful  method  of  separating  the  mineral  from  the 
oil  prevented  the  practical  application  of  these  early  patents.  Burn- 
ing the  oil  was  tried,  but  this  left  a  difficult  residue  to  treat,  and  the 
large  consumption  of  oil  made  the  method  too  expensive.  Settling 
the  mineral  out  by  thinning  the  oil  with  gasoline,  ether,  carbon- 
bisulphide,  etc.,  also  proved  too  expensive,  and  it  was  not  until  July 
1900  that  this  difficulty  was  overcome,  when  Mr.  Francis  E.  Elmore, 
of  Leeds,  England,  accomplished  the  separation  by  means  of  a  cen- 
trifugal machine,  similar  in  most  respects  to  those  used  in  sugar 
factories  and  in  milk  and  cream  separation.  This  contribution  by 
Mr.  Elmore,  then,  made  the  process  feasible/7 

[They  give  an  illustration  of  the  plant  designed  by  the  Oil  Con- 
centration Syndicate  and  describe  the  operations.  Their  own  ap- 
paratus is  shown  in  photographs  and  they  give  details  of  the  tests 
made  on  various  ores.  In  brief,  they  obtained  the  following  results : 

Extrac- 
Character  of  ore.  tion,  % 

Gold-quartz   ore    86 

Silver  ore  75 

Copper-schist  tailing  90 

Molybdenite  ore   75 


FROTH    AND   FLOTATION  103 

They  describe  the  nature  of  their  experiments  and  comment  on  the 
facts  disclosed  in  a  most  intelligent  way.  "We  quote  the  salient  para- 
graphs.] 

' '  In  making  a  test,  the  ore  is  first  crushed  to  the  desired  fineness, 
and  the  proper  charge  is  thoroughly  wetted  in  the  solution  to  be  used 
(usually  water),  thus  forming  a  thin  pulp.  The  oil  is  next  added 
and  the  whole  charge  thoroughly  mixed.  This  mixing,  or  agitation, 
can  be  done  in  two  different  ways:  The  charge  may  be  agitated  very 
gently,  the  oil  being  kept  in  a  single  lake,  and  broken  up  as  little  as 
possible  consistent  with  a  thorough  contact  of  pulp  and  oil;  or  the 
charge  may  be  agitated  so  violently  as  to  dash  the  oil  up  into  a  foam 
or  froth,  full  of  air  bubbles ;  thus  a  very  thorough  contact  of  oil  and 
pulp  is  obtained.  ****** 

' '  Three  methods  of  mixing  may  be  used. 

1.  By  inverting  the  tube  several  times,  thus  allowing  the  ore  to 
fall  through  the  oil. 

2.  By  rotating  the  tube  in  a  horizontal  position,  thus  throwing 
the  pulp  up  on  to  the  surface  of  the  lake  of  oil. 

3.  By  violently  shaking  the  tube,  thus  producing  the  foam  effect* 
or  at  least  shattering  the  oil  into  small  globules." 

•  '••**•>• 

"The  solution  used  in  the  concentration  is  a  matter  of  some  im- 
portance. Water  is,  of  course,  used  whenever  possible,  but  certain 
other  solutions  have  important  advantages.  As  before  stated,  an 
acid  solution  is  found  advantageous.  It  cleans  the  metallic  surfaces 
by  dissolving  the  metallic  oxide  coatings  that  may  have  formed  on 
them.  It  increases  the  specific  gravity  of  the  solution,  and  it  aids  in 
producing  the  foam  effect,  which  is  due  to  the  generation  of  certain 
gases. 

As  before  stated,  the  specific  gravity  of  the  average  oil  used  is 
about  0.9  and  water  1.0, f  leaving  a  difference  of  about  0.1  for  buoy- 
ancy or  carrying  capacity  of  the  oil. 

The  idea  at  once  suggests  itself  that  if  a  denser  solution  be  used, 
the  carrying  power  of  the  oil  will  be  increased  correspondingly.  A 
salt  (NaCl)  solution,  for  instance,  gives  excellent  results.  A  saturated 
solution  of  NaCl  at  20° C.,  containing  about  27%  NaCl,  has  a  specific 
gravity  of  1.204.  This  gives  a  difference  of  0.3  between  the  specific 
gravities  of  the  oil  and  of  the  solution,  and  a  carrying  capacity  of 
the  oil  threefold  greater  than  with  water  alone.  Not  only  does  it 


*[The  italics  in  all  these  quotations  are  ours. — EDITOR.] 
t[In  the  original  it  is  .1. — EDITOR.] 


104  THE  FLOTATION  PROCESS 

give  greater  buoyancy  to  the  oil,  but  it  also  aids  materially  in  pro- 
ducing the  foam  effect,  and  probably  aids  in  brightening  the  metallic 

surfaces. ' ' 

****** 

As  a  conclusion  to  the  above  experiments,  the  following  sugges- 
tions and  inferences  are  appended : 

1.  As  REGARDS  THE  WETTED  PULP.  As  far  as  could  be  determined, 
particles  with  either  metallic  or  non-metallic  surfaces,  when  in  a  dry 
state,  alike  adhere  to  the  oil.  Furthermore,  there  is  no  affinity  of  oil 
for  water,  as  shown  by  the  fact  that  an  oiled  surface  cannot  be  wetted. 
Hence  if  a  metallic  particle  be  thoroughly  wetted,  a  water  surface 
and  not  a  metallic  surface  is  exposed  to  the  oil;  and  the  former,  as 
before  stated,  has  no  affinity  for  the  oil.  It  is  evident  then  that  the 
water  film  must  first  be  displaced  before  the  oil  and  mineral  can 
come  in  contact  with  each  other.  This  displacement  is  hardly  prob- 
able if  the  water  film  is  in  intimate  contact  with  the  particle,  and  it 
seems  more  probable  that  the  differentiation  is  due  to  the  fact  that 
non-metallic  surfaces  are,  and  metallic  surfaces  are  not,  actually 
wetted.  If  this  be  the  case,  a  careful  study  of  the  relative  wetting 
of  different  surfaces  would  be  an  important  line  of  investigation. 

2.  The  ratio  of  the  exposed  surface  to  the  weight  of  the  particle 
should  be  as  large  as  possible,  because  the  total  adhesive  force  is 
increased  with  an  increase  of  the  surface  exposed  to  contact  with  the 
oil.    This  condition  is  best  realized  when  the  mineral  breaks  up  into 
thin  flakes.     It  is  evident  from  this  that  a  knowledge  of  the  fissile 
character  of  the  minerals  in  question  is  important. 

3.  One  fundamental  difficulty  involved  in  this  process  is  that  it 
undertakes  to  concentrate  and  float  a  heavy  metallic  mineral,  and 
sink  the  lighter  gangue  minerals,  but  this  point  is  not  necessarily 
fatal  to  the  process.     It  is  evident,  however,  that  the  heavier  the 
gangue  and  the  lighter  and  more  fissile  the  metallic  minerals,  the 
better  the  ore  is  adapted  to  this  method  of  concentration.     This  is  a 
direct  reversal  of  the  ideal  conditions  for  jig  or  vanner  concentration. 

4.  Another  characteristic  of  the  process  is  the  fact  that  the  ratio 
of  concentration  is  usually  small,  due  to  the  large  amount  of  gangue 
occluded  by  the  oil  and  carried  into  the  concentrates.    This  difficulty 
is  increased  by  sliming  the  gangue  minerals.    Sliming  of  the  metallic 
minerals  is  no  disadvantage. 

FOAM  EFFECT. — The  foam  effect  is  produced  by  a  violent  agita- 
tion, especially  in  acid  or  salt  solutions.  This  throws  the  oil  into  a 
froth,  which  is  heavily  charged  with  air  or  other  gases.  This  gas,  of 


FROTH    AND    FLOTATION  105 

course,  gives  a  greatly  increased  buoyant  force.  The  oil  in  this  condi- 
tion assumes  a  certain  load  of  mineral  and  holds  it  in  a  very  stable 
condition.  The  charge  does  not  settle  and  overload  on  standing  as 
in  the  case  of  the  lake  effect.  The  foam  effect  is  best  adapted  for 
light  flaky  minerals,  such  as  molybdenite. 

The  work  above  outlined  suggests  many  lines  of  further  investi- 
gation, and  as  these  come  to  be  worked  out,  the  process  will  become 
more  valuable  and  of  more  general  application." 

[It  is  clear  that  they  had  a  good  idea  of  the  usefulness  of  the 
froth,  and  how  to  make  it.  In  the  employment  of  salt  and  acid,  they 
anticipated  G.  D.  Delprat,  for  his  British  patent  for  the  use  of  salt 
and  sulphuric  acid  was  taken  out  on  December  11,  1903,  that  is,  two 
months  after  this  article  was  published.  The  early  work  of  C.  V. 
Potter  (patented  on  January  14,  1902)  and  G.  D.  Delprat  (beginning 
with  a  patent  dated  November  28,  1902)  did  not  involve  the  use  of 
oil,  but  the  generation  of  gas  in  the  pulp  to  form  bubbles.  Alcide 
Froment  (under  patent  dated  June  4,  1902)  connected  the  oil  and 
bubble  ideas,  and  it  is  his  patent  that  forms  the  basis  of  the  Minerals 
Separation  process,  to  which  in  1905  (and  particularly  November  6, 
1906)  were  added  several  patents  obtained  by  H.  L.  Sulman,  H.  F. 
K.  Picard,  and  John  Ballot,  for  the  agitation-froth  process.  Thus 
these  three  students  at  the  University  of  California  had  touched  upon 
an  idea  destined  to  be  of  the  greatest  importance  in  metallurgy,  but 
they  did  not  know  it.  In  the  very  same  issue  of  their  Journal  of 
Technology  there  appears  an  article  on  'The  Method  of  Obtaining 
Letters  Patent.'  The  irony  of  the  juxtaposition  is  evident  now.  We 
note  that  the  manager  of  this  student  publication  was  Arthur  H. 
Halloran,  then  a  junior  in  the  University.  He  became  a  member  of 
the  staff  of  the  Mining  and  Scientific  Press  after  graduation  and  for 
some  time  after  his  father,  J.  F.  Halloran,  sold  the  control  of  the 
paper  to  the  present  writer.  However,  it  may  not  be  so  surprising 
that  these  young  fellows  failed  to  appreciate  the  importance  of  the 
suggestions  obtained  in  the  course  of  their  experimental  work,  but  it 
is  truly  remarkable  that  a  keen  investigator  like  their  professor,  the 
late  Samuel  B.  Christy,  should  have  overlooked  it,  at  a  time,  too,  when 
he  himself  was  at  work  on  kindred  research,  more  particularly  in 
cyanidation.  It  may  have  been  his  absorption  in  the  one  part  of  the 
subject  that  prevented  him  from  obtaining  the  right  focus  on  these — 
now,  to  us — deeply  suggestive  experiments. — EDITOR.] 


106  THE  FLOTATION  PROCESS 


FLOTATION  AT  WASHOE  REDUCTION  WORKS,  ANACONDA 

By  E.  P.  MATHEWSON* 
(From  the  Mining  and  Scientific  Press  of  August  28,  1915) 

The  mineral  that  is  two  millimetres  and  under  in  size  is  sent 
to  the  Hardinge  mills  for  re-grinding.  These  mills  are  10  ft.  diam. 
by  4  ft.  long,  and  are  in  closed  circuit  with  simplex  Dorr  classifiers, 
one  classifier  to  each  mill,  6  mills  to  the  section,  and  8  sections  in 
the  establishment. 

The  overflow  from  the  classifiers  goes  to  the  flotation  division, 
and  the  classifier-sand  is  returned  to  the  Hardinge  mills.  At  present 
pebbles  are  being  used  in  the  Hardinge  mills,  but,  in  all  probability, 
steel  balls  will  ultimately  be  used.  With  pebbles  the  Forbes  lining 
is  used,  but  with  steel  balls  in  use,  each  mill  will  be  fitted  with  a 
false  wooden  lining  to  reduce  the  diameter  of  the  cylinder,  and 
a  manganese-steel  lining  will  be  placed  inside  of  this. 

Each  mill  has  a  direct-connected  225-hp.  motor.  The  mill  fitted 
with  pebbles  required  from  95  to  115  hp.,  but  the  motors  are  made 
extra  heavy,  in  anticipation  of  the  use  of  steel  balls. 

In  each  section  of  the  flotation  plant  there  are  four  Minerals 
Separation  machines,  each  having  15  agitators  and  14  floating- 
compartments.  Below  these  are  six  Callow  cells  for  cleaning  the 
concentrate.  The  agitators  (or  the  Minerals  Separation  machines 
are  made  of  gun-metal  and  are  driven  by  bevel-gears  from  the  main 
shaft.  (See  Fig.  17.)  Each  machine  is  driven  independently  by  a 
150-hp.  motor,  running  at  385  r.p.m.  on  full  load.  The  speed  of 
the  agitators  is  reduced  to  about  225  r.p.m. 

The  product  from  the  machines  is  a  tailing,  which  goes  to  waste 
(from  this  tailing,  fire-brick,  building-brick,  and  acid-proof  brick 
will  be  made  in  a  new  brick-plant  now  under  construction)  ;  a 
concentrate,  which  is  sent  to  the  Dorr  thickener-tanks,  for  settle- 
ment— this  comes  from  the  first  three  cells  of  the  frothing-machines. 
The  rough  concentrate  from  the  next  six  cells  of  the  M.  S.  machines, 
is  further  cleaned  in  the  Callow  cells  (See  Fig.  18),  making  a  clean 
concentrate;  and  the  middling,  which,  with  the  middlings  from 
the  remaining  five  cells  of  the  M.  S.  machines,  is  returned  to  the  feed 
of  these  same  machines. 

About  6  to  8  Ib.  of  50°  B.  sulphuric  acid,  per  ton  of  flotation- 


*Manager  for  the  Anaconda  Copper  Mining  Company. 


FLOTATION   AT  THE  WASHOE  REDUCTION  WORKS,  ANACONDA         107 


110  THE  FLOTATION  PROCESS 

to  the  other.  For  instance,  the  No.  2  section  of  the  mill  was  in 
operation  on  the  26th  day  of  May  for  ordinary  water-concentration ; 
but  was  wholly  re-constructed  and  in  operation,  using  the  flotation 
process,  on  the  26th  day  of  June.  Each  section  has  a  capacity  of 
2000  tons  of  original  feed  daily.  At  the  present  rate  of  re-construction 
the  entire  plant  will  be  re-modeled  by  January  1,  1916. 


FLOTATION  AT  THE  CENTRAL  MINE,  BROKEN  HILL 

By  JAMES  HEBBARD* 
(From  the  Mining  and  Scientific  Press  of  September  4,  1915) 

fEARLY  ATTEMPTS  AT  FROTHING.  While  concentrating  the  galena 
in  the  lead  ore  produced  from  the  Central  mine,  a  valuable  by-product 
was  obtained  in  the  form  of  slime  assaying  18%  lead,  20%  zinc, 
and  16  oz.  silver  per  ton.  This  came  from  an  ore  in  which  quartz 
and  rhodonite  were  the  chief  gangue-minerals.  In  the  course  of 
ordinary  operations,  it  had  long  been  observed  that  a  froth  was 
formed  containing  high  metallic  values,  in  silver  and  lead  par- 
ticularly, whenever  conditions  were  favorable,  as,  for  instance, 
where  the  rotation  of  trommels,  or  the  splash  of  the  elevators  or 
raff-wheels,  or  the  motion  of  the  jig-plungers,  produced  a  violent 
agitation  of  the  mill-water  containing  slime.  Early  in  1901  a  series 
of  experiments  was  carried  out  for  the  purpose  of  reproducing  and 
accentuating  the  conditions  responsible  for  this  valuable  float- 
concentrate.  Experiments  and  tests,  extending  over  several  months, 
were  made  on  slimes  of  varying  degrees  of  fineness.  Among  the 
appliances  tried  was  a  series  of  funnel-shaped  vessels  with  the  small 
ends  downward,  each  fitted  with  an  overflow-lip.  The  bottom  end 
of  the  funnel  or  cone-shaped  vessel  was  fitted  with  a  tap  or  plug 
discharging  the  contents  into  the  next  vessel  in  the  series,  and  so  on. 
To  each  vessel  was  attached,  near  the  bottom,  a  water-pipe,  as  well 
as  a  pipe  carrying  compressed  air.  The  object  of  the  water  was 
to  provide  an  upward  current  for  the  contents  of  the  vessel,  while 
the  object  of  the  compressed  air  was  to  produce  agitation,  and 


*Manager  of  the  Central  Mine,  Broken  Hill,  New  South  Wales. 
fAbstract  of  paper  appearing  in  the  Proceedings  of  the  Australasian  Insti- 
tute of  Mining  Engineers,  November  10,  1913. 


FLOTATION  AT   THE   CENTRAL  MINE,    BROKEN   HILL 


111 


enhance  the  agitation  effect  of  the  up-current  of  water,  in  the 
expectation  of  reproducing  the  conditions  causing  the  'float'  or 
metallic  froth.  Speaking  generally,  these  experiments  were  on  the 
lines  of  a  spitzkasten,  with  a  strong  up-current  to  produce  an 
agitation  of  the  slime-water,  assisted  by  jets  of  compressed  air.  It 
was  thus  early  recognized  that  the  bubbles  of  froth  noticed  in 
the  wet-concentration  operations  were  due  to  the  aeration  produced 
by  violent  agitation,  resulting  from  mechanical  implements  moving 
rapidly  in  water.  In  these  experiments  a  metallic  froth  or  scum 
could  be  produced  and  recovered  assaying  26  oz.  silver,  30%  lead, 
and  22%  zinc.  The  appliance  employed  is  illustrated  in  Fig.  19. 


FIG.    19.      APPARATUS   FOB  EXPERIMENTS   ON    FROTH. 

[Up  to  that  time  the  lead  concentrate  was  the  only  marketable 
product  from  the  ordinary  water  concentration.  Besides  calcite, 
the  ore  contained  a  good  deal  of  rhodonite  and  garnet,  each  of  which 
has  a  specific  gravity  close  to  that  of  blende.  Thus  water  concentra- 
tion could  only  yield  a  quartz  tailing  and  a  leady  zinc-rhodonite- 
garnet  middling.] 

PRELIMINARY  TEST.  Early  in  1903  an  exhaustive  series  of  labora- 
tory tests  was  made  on  the  lead  by-product  by  flotation  methods, 
using  heated  sulphuric  acid  and  salt-cake  solution.  These  tests 


112  THE  FLOTATION  PROCESS 

yielded  some  slight  measure  of  success  on  material  specially  prepared, 
that  is,  on  grainy  material  from  which  both  the  coarse  and  fine  had 
been  eliminated,  leaving  it  evenly  sized.  Certain  classes  of  the 
material  produced  by  our  mills  contained  such  a  large  proportion 
of  carbonates — such  as  carbonates  of  manganese,  lime,  and  lead — 
that  no  flotation  could  be  secured  except  by  a  prohibitive  consumption 
of  acid.  These  tests  were  carefully  made,  but  the  best  work  done 
in  the  laboratory  was  not  equal  to  that  being  secured  on  a  commercial 
scale  in  the  existing  magnetic  plant.  The  tests  on  these  flotation 
methods  were  conductel  in  pans  or  vessels  worked  on  the  principles 
of  spitzkasten,  following  the  lines  of  Potter  and  Delprat.  The  first 
apparatus  was  constructed  so  that  the  liquors  could  be  raised  in 
temperature  by  the  application  of  direct  heat  underneath  the  pan; 
but  in  the  later  types  the  temperature  of  the  liquor  in  the  pan 
or  spitz-box  was  maintained  by  the  injection  of  live  steam  into  the 
storage-tank.  In  none  of  these  tests  was  agitation  employed,  the 
material  to  be  treated  being  fed  practically  dry  on  the  surface  of 
the  liquor  in  a  regular  stream,  and  the  heated  liquor  added  through 
a  pipe  discharging  near  the  bottom  of  the  vessel,  and  given  an 
upward  inclination  in  order  to  produce  an  up-current  in  the  box 
itself  and  a  gentle  overflow  at  the  lip.  A  still  surface  was  imperative 
in  this  operation,  and  it  was  equally  evident  that  the  operation 
.depended  largely  for  its  success  on  surface  tension  of  the  liquor, 
after  the  gas  evolved  by  the  action  of  the  acid  on  the  mineral 
carbonates  had  raised  the  particles.  This  surface  tension  was 
increased  by  the  density  attained  in  the  one  case  by  the  salts  formed 
from  the  mineral  and  gangue  through  the  action  of  the  sulphuric 
acid,  and  in  the  other  by  the  addition  of  salt-cake.  In  all  these 
experiments  the  liquor  was  returned  by  the  ordinary  type  of  air-lift, 
using  compressed  air  at  about  70-lb.  pressure.  These  experiments 
definitely  demonstrated : 

1.  That  there  was  a  limit  to  the  size  of  the  particle  that  could 
be  buoyed  up. 

2.  That  any  material  below  a  certain  size,  no  matter  what  its 
character — whether  gangue  or  mineral — floated,  owing  to  the  density 
of  the  solution. 

3.  That  if  the  finer  particles  of  gangue  were  not  eliminated 
before  treatment  they  would  be  floated  with  the  mineral,  and  lower 
its  value  in  metals  to  such  an  extent  as  to  make  it  unmarketable. 

Slime,  whether  existing  as  a  by-product  of  the  ordinary  wet-mill 
concentration   or  subsequently   produced   in   preparing   tailing   for 


FLOTATION  AT   THE   CENTRAL  MINE,    BROKEN   HILL  113 

treatment,  bulked  so  largely  among  the  total  material  available  for 
re-treatment  that  any  process  that  failed  in  this  direction  was  too 
limited  in  its  scope  to  be  of  much  value  to  the  Central  mine. 

As  far  as  any  process  up  to  date  was  concerned,  slime  had  to 
be  regarded  as  of  no  value  except  in  so  far  as  it  was  available  for 
smelting.  The  Broken  Hill  Proprietary  Co.  had  used  a  considerable 
quantity  in  this  way,  and  had  discovered  that  roasting  or  sin- 
tering the  slime  in  open  heaps  after  briquetting  gave  a  fair 
product  valuable  for  smelting,  a  good  deal  of  the  sulphur  and  a 
fair  proportion  of  the  zinc  having  been  driven  off.  The  Sulphide 
Corporation  also  sought  to  make  its  slime  available  by  this  means, 
but  it  was  proved  that  the  losses  of  metal  were  too  great  to  justify 
this  method  of  rendering  the  slime  amenable  to  direct  smelting. 

CATTERMOLE  OR  GRANULATION  PROCESS.  The  foregoing  experi- 
ments were  abandoned  on  account  of  information  received  from 
London.  C.  F.  Courtney,  who  was  in  England  during  the  year 
1902,  advised  that  a  discovery  of  considerable  importance  had  been 
made;  that  laboratory  trials  gave  every  indication  of  success  on  a 
large  scale ;  and  that  the  process  was  so  comprehensive  as  to  include 
the  finest  slime  and  varying  coarser  sizes  of  particles  up  to  f  mm. 
diam.  This  was  subsequently  known  as  the  Cattermole  or  granula- 
tion process,  and  consisted  in  the  agitation  of  a  mixture  of  pulp, 
oil,  and  water,  containing  a  suitable  acid,  or  an  alkali  with  soap 
or  other  emulsifying  agent,  so  as  to  agglomerate  the  oil-coated 
particles  into  granules.  The  oil  was  thus  employed  in  a  state  of 
emulsion  in  water  in  the  presence  of  an  emulsifying  agent,  such 
as  soap.  After  agitation  the  mixture  was  passed  into  an  up-current 
separator  or  classifier  to  remove  the  lighter  non-oil-coated  particles 
from  the  agglomerated  masses  of  oil-coated  particles.  The  lighter 
sand  having  been  eliminated,  the  pulp  passed  to  a  second  series 
of  agitators  to  increase  the  size  of  the  granules,  and  thence  to  a 
second  classifier  for  the  removal  of  the  heavy  sand.  From  the 
bottom  of  this  second  classifier  some  granulated  concentrate  was 
recovered,  but  the  heavy  sand  from  the  overflow  also  carried  over, 
with  the  up-current,  a  large  amount  of  granulated  mineral.  This 
mixture  of  granulated  mineral  and  heavy  sand  passed  then  to  a 
third  series  of  agitators,  and  thence  to  a  shaking  table,  where  the 
granulated  mineral,  rendered  more  buoyant  by  directing  jets  of 
compressed  air  onto  the  surface  of  the  moist  pulp,  was  buoyed  to 
the  surface  of  the  water  and  floated  off  the  bottom  of  the  table, 
while  the  gangue  sank  and  was  delivered  over  the  end  of  the  table. 


114  THE  FLOTATION  PROCESS 

In  order  to  give  this  process  a  thorough  trial,  a  model  plant 
was  sent  from  England  and  erected  on  the  mine  early  in  1904. 
G.  A.  Chapman  was  specially  appointed  to  conduct  experiments 
with  this  plant,  and  started  a  long  series  of  tests  early  in  June  of 
the  same  year.  It  was  quickly  demonstrated  that  the  process  was 
capable  of  making  high  recoveries  of  all  the  three  metals  from  the 
very  finest  slime,  whether  taken  from  the  current  work  of  the  mill 
or  from  old  accumulations,  and  also  that  old  tailing  or  new  crude 
ore  were  amenable  to  treatment  when  crushed  to  a  given  fineness. 
The  largest  size  of  particle  that  could  be  recovered  was  ascertained 
to  be  about  £  mm.,  thus  confirming  the  London  work;  but  it  was 
found  that  results  improved  with  a  decrease  in  size  to  impalpability. 

In  the  early  tests  by  Mr.  Chapman,  emulsions  of  the  heavy  oil 
of  petroleum  were  used,  but  the  cost  was  excessive,  and  it  was  found 
impossible  to  treat  slime  successfully.  Emulsions  of  fatty  acids, 
and  also  soft  soap,  were  then  tried,  but  proved  prohibitive  as  to 
cost,  except  in  the  case  of  oleic  acid.  Oleic-acid  emulsion  was  found 
to  act  rapidly  and  effectively  on  crude  ore  as  well  as  on  all  lead 
by-products,  including  slime. 

Mr.  Chapman 's  work  on  oils  and  the  results  obtained  by  him 
with  the  model  plant  using  the  granulation  process  were  satisfactory, 
but  it  was  thought  wise  to  have  these  confirmed  by  an  independent 
chemist,  and  therefore  J.  C.  Moulden,  the  company's  chief  metallur- 
gist at  Cockle  Creek,  was  called  in,  repeated  the  experiments,  and 
amply  confirmed  Mr.  Chapman's  work.  Later  it  was  found  possible 
also  to  reduce  the  quantity  of  oleic  acid,  as  was  proved  by  the 
following  tests  in  December  1904: 

Material  used  was  crushed  tailing  mixed  with  slime. 

Test  No.  1.  3.5%  oleic  acid  on  mineral  and  0.75%  sulphuric 
acid  circuit. 

The  cost  of  emulsion  in  this  case  was  10s.  per  ton  of  ore,  but 
the  results  were  excellent,  the  concentrate  being  recovered  as  partly 
granulated  and  partly  float  or  froth. 

In  test  No.  2,  only  0.75%  of  oleic  acid  with  the  same  (0.75%) 
sulphuric  acid  circuit,  in  which  case  the  cost  of  emulsion  amounted 
to  2s.3d.  per  ton  of  ore,  the  results  being  excellent,  with  all  float 
concentrate,  no  granular  material  being  formed.  This  test  took 
considerably  longer  in  agitation. 

ERECTION  OF  LARGE  PLANT.  Mr.  Chapman's  tests,  and  their 
confirmation  by  Mr.  Moulden,  established  the  fact  that  a  process 
was  obtained  that  would,  with  suitable  arrangements  for  crushing, 


FLOTATION  AT   THE   CENTRAL  MINE,    BROKEN   HILL  115 

efficiently  handle  the  whole  of  the  by-products  of  the  wet  mill, 
including  slime.  It  was  accordingly  decided  to  erect  a  plant  on 
the  lines  of  the  model,  with  slight  modifications  as  dictated  by 
experience,  capable  of  treating  100  tons  per  day,  operating  on  a 
commercial  scale. 

It  was  clear,  from  experiments  and  observations,  that  the  time 
of  agitation  was  a  factor  in  the  aeration  and  oiling  of  the  mineral 
particles.  Therefore,  reckoning  from  the  size  and  capacity  of  the 
mixers  in  the  model  plant,  a  mixer  was  built  of  the  following 
dimensions:  5  ft.  .deep  and  3  ft.  diam.,  with  a  wooden  stirrer 
2  ft.  6  in.  diam.  at  bottom  placed  vertically  and  made  to  revolve  at 
the  rate  of  350  r.p.m. 

Experiments  with  this  one  mixer  unit  indicated  that,  to  make 
the  treatment  continuous  for  the  stipulated  100  tons  per  day,  it 
would  be  necessary  to  have  for  the  first  unit  a  series  of  six  mixers 
in  order  to  allow  of  the  proper  cleaning  of  the  particles  and  the 
thorough  aeration  of  the  whole  mixture  before  the  discharge  of 
the  material  under  treatment  from  the  last  of  the  series.  The  mixer 
was  of  the  core-stirrer  type. 

Accordingly,  the  plant  was  designed  on  these  lines,  and  con- 
sisted of: 

1.  Grinding  apparatus. 

2.  Vat  for  emulsifying  various  oils. 

3.  Set  of  six  mixers  in  series. 

4.  Upcasts  for  separating  sand  and  float. 

5.  Second  set  of  mixers  for  further  aeration. 

6.  Upcasts  for  further  separation  of  sand  and  float. 

7.  Third  set  of  mixers  for  re-aeration. 

8.  Wilfley  tables  for  the  separation  of  coarse  sand  from  granu- 
lated sulphide. 

Early  in  1905  the  construction  of  this  plant  was  commenced;  it 
was  completed  at  a  cost  of  £11,000,  and  started  work  in  July  1905. 
The  method  of  treatment  adopted  was  on  the  lines  of  the  tests  made 
in  the  experiemental  model  plant,  and  may  be  briefly  described. 
See  Fig.  20. 

The  ore,  reduced  to  a  suitable  fineness,  was  elevated  to  a  hopper 
at  the  top  of  the  building  and  fed  into  No.  1  mixer,  where  it  was 
agitated  with  the  solution,  the  emulsion  (previously  prepared  on 
the  bottom  floor)  being  added  at  the  same  time,  together  with  further 
sulphuric  acid,  if  required.  The  feed  of  ground  material  and  the 
addition  of  the  circuit-liquor  and  reagents  was  maintained  constantly 


116 


THE   FLOTATION   PROCESS 


and  regularly.  After  passing  through  the  first  set  of  six  mixers  a 
pulp  consisting  of  ground  ore,  acidulated  water,  and  emulsion  was 
passed  to  a  hydraulic-sizing  appliance  known  as  an  upcast,  where 
the  slime-gangue  was  eliminated  by  overflowing.  The  balance  of 
the  mixture  was  passed  into  the  second  set  of  mixers,  beginning  with 
No.  7,  where  more  emulsion  and  sulphuric  acid  were  added  if 
necessary.  The  agitation  and  aeration  were  maintained  and  the  pulp 


-J 


FIG.  20.      THE  EXPEBIMENTAL  MODEL  PLANT. 


discharged  from  No.  9  into  another  upcast,  where  further  slime- 
gangue  was  eliminated  by  overflow.  The  balance  of  the  material 
was  then  passed  to  No.  10  mixer,  and  thence  through  No.  12  to 
the  Wilfley  tables.  The  separation  on  the  tables  was  effected  thus: 
Such  concentrate  as  had  been  frothed  by  the  aeration  and  agitation 
passed  off  the  table  immediately  opposite  the  point  of  feeding.  The 
granulated  or  'air-bally'  material  remained  in  close  contact  with 
the  table,  along  with  the  sand,  but  floated  immediately  under  the 
influence  of  puffs  of  air  (supplied  through  a  pipe  laid  lengthwise 
and  close  to  the  table),  and  then  floated  off  with  the  froth  concentrate. 
The  sand  was  delivered  toward  and  at  the  end  of  the  table,  thus 


FLOTATION  AT   THE  CENTRAL   MINE,    BROKEN   HILL  117 

exactly  reversing  the  relative  positions  of  concentrate  and  tailing 
as  ordinarily  obtained  if  working  by  gravity  concentration.  The 
slime  and  sand  were  collected  in  one  receptable  and  the  float  and 
granulated  concentrate  in  another,  the  surplus  liquors  in  each  case 
flowing  to  a  common  sump  for  re-use. 

From  the  first  day  of  operation  the  ease  with  which  the  float 
concentrate  could  be  recovered  was  very  striking;  but  the  separation 
of  the  granulated  concentrate  from  the  coarse  sand  by  tabling  on  a 
large  scale  was  found  to  be  a  very  delicate  and  difficult  operation, 
and  it  was  at  once  evident  that  *  spitz'  separation  would  relieve  the 
tables.  The  upcasts  were  also  continually  choking  and  proving  a 
source  of  trouble,  besides  sending  over  large  quantities  of  slime 
with  the  concentrate,  thus  reducing  the  grade  of  the  product  and 
lessening  its  market- value. 

It  was  therefore  decided,  when  the  plant  had  been  running  for  a 
few  days  only,  to  construct  a  small  rectangular  spitz-box  for  trial. 
This  was  introduced  early  in  August  1905,  the  feed  to  the  spitz-box 
being  prepared  pulp  discharged  from  No.  7  mixer. 

It  was  found  also,  as  soon  as  the  plant  started  regular  treatment, 
that  the  agitation  was  excessive,  and  mixers  10,  11,  and  12  were 
cut  out. 

Cone-agitators  made  of  phosphor  bronze  were  tried,  then  cen- 
trifugal stirrers,  but  the  scour  both  on  the  stirrer  and  the  sides  of 
the  mixer,  due  to  the  impact  of  the  sand,  was  so  great  that  these  had 
to  be  abandoned,  although  the  agitation  and  aeration  had  been  con- 
siderably increased. 

The  spitz-box  in  the  slime-overflow  circuit  gave  excellent  results, 
and  toward  the  end  of  August  it  was  possible  to  obtain  the  requisite 
agitation  by  using  the  first  six  mixers  only.  A  fresh  spitz-box  was 
placed  in  the  position  formerly  occupied  by  vats  7  and  8,  with  ar- 
rangements for  all  tailing-flows,  both  slimes  and  sands,  to  deliver  to 
No.  1  hutch  of  a  special  spitz  on  the  floor  beneath.  The  object  of  this 
spitz  (3-compartment)  was  (1)  to  allow  a  settlement  of  the  granu- 
lated material  in  the  first  compartment;  (2)  to  effect  a  settlement  of 
middling  for  re-treatment  on  tables  in  the  second;  (3)  to  provide  for 
the  deposition  of  clean  sand  and  slime  in  the  third,  with  an  un- 
restricted overflow  for  the  float  material.  Sprays  on  the  surface  of 
the  liquor,  and  upcasting  jets  of  water,  were  provided  to  assist  the 
operation.  Various  simplified  forms  were  later  adopted  as  the  process 
merged  from  partial  to  complete  flotation,  as  illustrated  in  the  ex- 
perimental spitz-box  for  the  granulation  plant  (Fig.  21). 


116 


THE   FLOTATION    PROCESS 


and  regularly.  After  passing  through  the  first  set  of  six  mixers  a 
pulp  consisting  of  ground  ore,  acidulated  water,  and  emulsion  was 
passed  to  a  hydraulic-sizing  appliance  known  as  an  upcast,  where 
the  slime-gangue  was  eliminated  by  overflowing.  The  balance  of 
the  mixture  was  passed  into  the  second  set  of  mixers,  beginning  with 
No.  7,  where  more  emulsion  and  sulphuric  acid  were  added  if 
necessary.  The  agitation  and  aeration  were  maintained  and  the  pulp 


<_v _.-fr.  CONCENTRATES  FLOAT  AND    1_ 

I * 1"       GRANULATED J 


FIG.  20.      THE  EXPEBIMENTAL  MODEL  PLANT. 

discharged  from  No.  9  into  another  upcast,  where  further  slime- 
gangue  was  eliminated  by  overflow.  The  balance  of  the  material 
was  then  passed  to  No.  10  mixer,  and  thence  through  No.  12  to 
the  "Wilfley  tables.  The  separation  on  the  tables  was  effected  thus: 
Such  concentrate  as  had  been  frothed  by  the  aeration  and  agitation 
passed  off  the  table  immediately  opposite  the  point  of  feeding.  The 
granulated  or  'air-bally'  material  remained  in  close  contact  with 
the  table,  along  with  the  sand,  but  floated  immediately  under  the 
influence  of  puffs  of  air  (supplied  through  a  pipe  laid  lengthwise 
and  close  to  the  table),  and  then  floated  off  with  the  froth  concentrate. 
The  sand  was  delivered  toward  and  at  the  end  of  the  table,  thus 


FLOTATION  AT   THE  CENTRAL  MINE,    BROKEN   HILL  117 

exactly  reversing  the  relative  positions  of  concentrate  and  tailing 
as  ordinarily  obtained  if  working  by  gravity  concentration.  The 
slime  and  sand  were  collected  in  one  receptable  and  the  float  and 
granulated  concentrate  in  another,  the  surplus  liquors  in  each  case 
flowing  to  a  common  sump  for  re-use. 

From  the  first  day  of  operation  the  ease  with  which  the  float 
concentrate  could  be  recovered  was  very  striking ;  but  the  separation 
of  the  granulated  concentrate  from  the  coarse  sand  by  tabling  on  a 
large  scale  was  found  to  be  a  very  delicate  and  difficult  operation, 
and  it  was  at  once  evident  that  'spitz'  separation  would  relieve  the 
tables.  The  upcasts  were  also  continually  choking  and  proving  a 
source  of  trouble,  besides  sending  over  large  quantities  of  slime 
with  the  concentrate,  thus  reducing  the  grade  of  the  product  and 
lessening  its  market- value. 

It  was  therefore  decided,  when  the  plant  had  been  running  for  a 
few  days  only,  to  construct  a  small  rectangular  spitz-box  for  trial. 
This  was  introduced  early  in  August  1905,  the  feed  to  the  spitz-box 
being  prepared  pulp  discharged  from  No.  7  mixer. 

It  was  found  also,  as  soon  as  the  plant  started  regular  treatment, 
that  the  agitation  was  excessive,  and  mixers  10,  11,  and  12  were 
cut  out. 

Cone-agitators  made  of  phosphor  bronze  were  tried,  then  cen- 
trifugal stirrers,  but  the  scour  both  on  the  stirrer  and  the  sides  of 
the  mixer,  due  to  the  impact  of  the  sand,  was  so  great  that  these  had 
to  be  abandoned,  although  the  agitation  and  aeration  had  been  con- 
siderably increased. 

The  spitz-box  in  the  slime-overflow  circuit  gave  excellent  results, 
and  toward  the  end  of  August  it  was  possible  to  obtain  the  requisite 
agitation  by  using  the  first  six  mixers  only.  A  fresh  spitz-box  was 
placed  in  the  position  formerly  occupied  by  vats  7  and  8,  with  ar- 
rangements for  all  tailing-flows,  both  slimes  and  sands,  to  deliver  to 
No.  1  hutch  of  a  special  spitz  on  the  floor  beneath.  The  object  of  this 
spitz  (3-compartment)  was  (1)  to  allow  a  settlement  of  the  granu- 
lated material  in  the  first  compartment;  (2)  to  effect  a  settlement  of 
middling  for  re-treatment  on  tables  in  the  second;  (3)  to  provide  for 
the  deposition  of  clean  sand  and  slime  in  the  third,  with  an  un- 
restricted overflow  for  the  float  material.  Sprays  on  the  surface  of 
the  liquor,  and  upcasting  jets  of  water,  were  provided  to  assist  the 
operation.  Various  simplified  forms  were  later  adopted  as  the  process 
merged  from  partial  to  complete  flotation,  as  illustrated  in  the  ex- 
perimental spitz-box  for  the  granulation  plant  (Fig.  21). 


118  THE  FLOTATION  PROCESS  . 

At  first  the  sand  was  ejected  by  sluicing  out  to  a  dam;  but  this 
being  wasteful  of  circuit-liquor,  and  therefore  also  acid,  it  was  de- 
cided to  construct  sand-boxes,  through  which,  in  turn,  the  suspended 
sand  could  be  deposited — the  liquor  overflowing  from  these  sand- 
boxes to  be  run  to  the  pump-sump  and  thence  re-circulated  through 
the  plant.  By  this  means  a  closed  circuit  would  be  secured,  and  liquor- 
losses  minimized.  It  was  not  until  November  that  these  sand-boxes 
were  actually  in  use.  Meantime,  it  was  noted,  particularly  in  slime- 
tests,  that  the  operation  was  appreciably  assisted  by  raising  the  tem- 
perature of  the  liquor.  Steam  jets  were,  therefore,  introduced  into 
the  mixers  in  the  plant  early  in  September  1905. 


FlG.    21.      EXPEBIMENTAL    SPITZ-BOX. 

Before  advancing  further  with  the  evolution  of  the  process  as  de- 
veloped in  the  first  large  plant,  it  is  perhaps  advisable  to  refer  here 
to  certain  experiments  that  mark  a  most  important  era  in  the  history 
of  the  process. 

DISCOVERY  OF  THE  FROTHING  PROCESS.  We  now  come  to  a  stage 
when  a  remarkable  development  in  the  operation  was  discovered 
(strangely  enough,  at  the  same  time  both  here  and  in  the  Patent 
Co.'s*  laboratory  in  London),  which  had  for  its  main  principle  the 
reversal  of  all  previous  operations,  and  consisted  in  the  complete 
flotation  of  each  particle  of  mineral  independently  in  place  of  granu- 
lating the  mineral  particles  and  causing  them  to  sink,  thus  not  only 
revolutionizing  the  process,  but  greatly  simplifying  and  cheapening  it. 
The  developments  noted  were  mainly  along  the  line  of  decreased  con- 
sumption of  oleic  acid  or  oil,  for  example,  from  3%  oleic  on  ore,  re- 
sulting in  very  little  float,  down  to  1%,  giving  practically  a  complete 
float. 

The  following  data  from  a  report  furnished  by  A.  H.  Higgins 
(March  16,  1905),  indicate  in  more  detail  the  nature  of  the  experi- 

*  [Minerals  Separation  Ltd. — EDITOR.] 


FLOTATION  AT   THE  CENTRAL   MINE,    BROKEN   HILL  119 

ments  and  the  effect  on  the  separation  produced  by  varying  the  per- 
centage of  oleic  acid. 

DETAILS  OF  EXPERIMENTS 

Time 

Percentage       for  Temper- 
Acid,        Oleic,          of  oleic     aeration,  ature, 
%              c.c.            on  ore.          min.  C.                         Remarks. 
1.1              15                 3.0                4  30.5°  Very  little  float 
1.1                7.5              1.5                4£  31.0°  Rather  more  float 
1.1                5.2              1.04              6  31.0°  Still  more  float 
1.1                3.1              0.62              6  32.0°  Still  more  float 
1.1                1.66            0.32              7  31.0°  Float  vastly  increased 
1.1                0.5              0.10              8  31.0°  Float  vastly  increased 

In  every  case  the  oleic  acid  has  been  measured  in  cubic  centimetres 
and  the  percentages  calculated  as  though  they  weighed  grains ;  but,  as 
the  specific  gravity  of  oleic  is  less  than  that  of  water  (taken  as  1),  all 
percentages  will  be  lower  than  those  actually  given. 

These  experiments  obviously  proved  that  the  reduction  in  the  per- 
centage of-  oleic  acid  materially  altered  the  type  or  character  of  the  oil- 
ing of  the  mineral  particles — the  higher  percentage  producing  gran- 
ules, which  were  precipitated,  while  the  lower  percentages  produced  a 
mineral  froth.  As  the  quantity  of  oleic  acid  decreased,  the  time  re- 
quired for  oiling  the  mineral  particles  and  aerating  them  was  found 
to  increase,  and  more  froth  formed.  These  tests,  followed  by  many 
others,  led  to  Messrs.  Sulman,  Picard,  and  Ballot's  British  patent  of 
April  12,  1905,  under  which  "finely  powdered  ore,  suspended  in 
acidified  water,  is  mixed  with  a  small  proportion  of  an  oily  substance 
such  as  oleic  acid,  amounting  to  a  fraction  of  1%  on  the  ore,  and 
agitated  until  the  oil-coated  minerals  form  into  a  froth,  which  can  be 
separated  from  the  gangue  by  flotation.  Heat  may  be  applied  to 
facilitate  oiling,  and  either  shaking  tables  or  spitz-boxes  may  be  used 
to  separate  the  frothy  mineral  from  the  sands  and  the  gangue  slime. " 

To  return  now  to  the  record  of  operations  at  the  large  plant,  some 
successful  tests  were  carried  out  in  September  1905  on  dump-slime, 
by  using  this  flotation  method.  Agitation  was  completed  in  six  mix- 
ers (using  cones)  in  0.6  to  \%  sulphuric  acid  at  a  temperature  of 
80-90° P.  The  quantity  of  oleic  acid  used  in  these  tests  was  from 
015  to  0.2%  on  the  actual  dry  weight  of  slime  treated.  From  the 
sixth  mixer  the  pulp  passed  "with  a  good  splash"  to  the  first  spitz, 
and  the  residues  from  this  "with  a  good  splash"  to  No.  2  spitz,  and 
the  tailing  from  this  latter  spitz-box  was  run  into  dams.  These  and 
other  experiments  emphasized  the  importance  of  dropping  the  pulp 


120  THE  FLOTATION  PROCESS 

vertically  into  the  spitz  to  assist  aeration  and  subsequent  flotation, 
and  of  heating  the  liquor  to  enhance  the  oiling  of  mineral  particles. 

The  three-compartment  spitz-box  with  upcast  water-flows  gave 
place,  in  turn,  to  a  two-compartment  spitz-box  without  upcast  flow, 
and  this,  in  turn,  was  replaced  by  a  single-compartment  spitz,  the 
latter  being  provided  with  a  rigid  flat  board  on  which  the  feed  was 
splashed  to  assist  aeration.  Conical  spitz-boxes  were  tried,  but  not 
generally  adopted. 

FROM  GRANULATION  TO  FLOTATION.  The  plant  had  now  been 
running  for  a  couple  of  months  on  tailings  and  slimes  from  various 
sources,  and  during  this  time  the  frothing  method  was  generally 
ousting  the  granulation  process,  until,  finally,  the  superiority  of  the 
spitz-box  and  froth  method  was  clearly  demonstrated.  The  Wilfley 
tables  of  the  original  plant  were  then  dismantled  to  make  room  for 
the  sand-boxes  already  mentioned,  and  the  granulation  gave  way  to 
flotation  with  simple  spitz-boxes  early  in  October,  after  treatment  of 
approximately  1700  tons  of  crude  ore,  tailing,  and  slime. 

This  method  of  working,  thus  briefly  outlined,  quickly  established 
itself  as  capable  of  dealing  with  the  company's  ores  and  by-products, 
and  Mr.  Chapman's  patent  of  September  1906  was  taken  out  to  pro- 
tect the  various  discoveries  made  by  supplementing  Sulman,  Picard, 
and  Ballot's  patent  (No.  5032,  1905) .  Under  Mr.  Chapman's  patent : 

1.  The  ore,  suitably  crushed,  is  agitated  with  acidified  water  in 
the  first  mixer  and  heated. 

2.  Oleic  acid  is  subsequently  added  in  the  second  vessel. 

3.  The  pulp  is  maintained  at  the  desired  temperature  in  the  third 
and  following  mixers,  with  violent  agitation  in  each  mixer  to  insure 
complete  and  thorough  aeration.     A  sequence  of  operations  is  thus 
arranged  by  which  the  solution,  after  the  second  agitator,  is  prac- 
tically or  entirely  neutralized,  so  that  the  liquor  in  circuit  as  a  whole 
is  neutral,  except  at  the  outset,  when  the  ore  is  introduced. 

The  adoption  of  this  flotation  process  with  its  neutral  liquor  al- 
lowed the  use  of  iron  where  formerly,  under  the  granulation  method, 
with  acid  liquor,  only  wood  or  special  metal  could  be  used.  For  in- 
stance, the  original  wooden-cone  mixers,  which  had  been  replaced  by 
centrifugal  stirrers  of  copper  or  beaters  of  regulus  metal,  were  now 
replaced  by  four-armed  stirrers  of  cast-iron. 

A  great  difficulty  lay  in  the  grinding.  The  experiments  had 
proved  that  the  best  work  could  be  obtained  on  material  that  would 
pass  through  40-mesh,  and  that  practically  the  finer  the  material 
the  better  the  recovery.  The  whole  experience  in  the  fine  grinding 


FLOTATION   AT   THE  CENTRAL  MINE,    BROKEN   HILL  121 

had  been  with  ball-mills  in  our  magnetic  plant,  and  accordingly  a 
No.  8  Krupp  dry  ball-mill  was  attached  to  this  plant  as  part  of 
the  equipment.  The  dry  mill  proved  unsuitable,  and,  with  consider- 
able difficulty,  it  was  converted  to  a  wet  mill.  Even  then  its  capacity, 
allowing  for  numerous  break-downs  partly  due  to  forcing  its  capacity, 
was  too  limited,  and  two  No.  5  Krupp  wet  ball-mills  were  installed 
to  assist.  Meantime,  experiments  proved  conclusively  that  grinding- 
pans  were  superior  in  character  of  work,  cost  of  maintenance,  and 
power  consumed,  to  the  ball-mills  for  re-grinding  tailing,  whereupon 
we  installed  a  grinding-plant  which  was  gradually  increased  until 
the  ball-mills  were  thrown  out  of  use  entirely.  The  character  of 
the  work  was  much  improved,  and  it  was  then  evident  how  much 
the  progress  of  the  process  to  a  satisfactory  stage  of  efficiency  had 
been  retarded  by  lack  of  efficient  grinding  appliances. 

EXTENSION  OF  PLANT.  The  operations  of  the  first  plant  were 
commercially  and  technically  successful,  and  an  extension  was 
completed,  with  all  its  appurtenances,  including  grinding-pans  for 
the  reduction  of  the  material  to  the  requisite  degree  of  comminution, 
conveyor-belts  for  the  disposal  of  the  residues,  together  with  bins 
for  concentrates  and  tanks  for  storage  of  liquor,  toward  the  end 
of  1906,  at  a  cost  of  £25,000,  the  sum  of  £11,000  having  been  already 
spent  on  the  initial  experimental  plant.  The  total  quantity  of 
material  treated  by  this  flotation  plant  was  135,8.08  tons,  which 
yielded  45,147  tons  of  high-grade  zinc  concentrate.  The  plant 
continued  in  successful  operation  until  the  completion  of  the  wet-mill 
zinc  section,  which  was  capable  of  supplying  the  quantity  of  zinc 
concentrate  under  contract.  During  the  time  this  plant  was  in 
operation  numerous  tests  were  made  with  a  view  to  increasing  the 
aeration,  which  was  recognized  as  the  chief  factor  in  flotation,  and 
at  the  same  time  lessening  the  mechanical  energy  absorbed  in  aerating. 
Among  these  may  be  mentioned  the  nest  of  centrtifugal  pumps,  as 
illustrated  in  Fig.  22.  The  pumps  were  worked  in  series,  each  one 
drawing  a  tailing  from  the  preceding  spitz  and  discharging  into 
the  next  succeeding  spitz.  The  aeration  and  flotation  were  produced 
satisfactorily,  but  it  was  soon  found  that  the  scour  in  the  pumps, 
caused  by  the  gritty  nature  of  the  material  being  pumped,  was 
so  great  that  the  heavy  maintenance  would  counter-act  the  other 
advantages.  Another  expedient  was  to  lift  the  whole  of  the  tailing 
discharged  from  the  first  spitz  by  means  of  an  air-lift.  This  also 
resulted  in  increased  aeration,  but  it  was  found  that  the  volume  of 
liquor  would  have  to  be  increased  to  an  impracticable  quantity  to 


122 


THE   FLOTATION    PROCESS 


give  the  necessary  velocity  to  carry  the  particles  of  ore,  etc.,  up 
the  rising  leg  of  the  pipe  and  prevent  settling.  An  elevator  was 
subsequently  installed  in  its  place  to  command  the  third  spitz  of  the 
series.  Further  expedients  were  the  insertion-  of  a  jet  of  air 
into  a  centrifugal  pump  used  for  raising  liquors  and  material  for 
re-treatment,  the  introduction  of  a  jet  of  compressed  air  into  the 


FIG.    22.      A   NEST  OF   CENTBIFUGAL  PUMPS. 

mixer-boxes,  and  also  the  insertion  of  pipes  in  the  mixer-boxes  in 
such  a  position  that  air  would  be  drawn  into  the  bottom  of  the 
mixer  by  the  rotation  of  the  blades.  As  a  result  of  all  these 
expedients,  the  conclusion  was  formed  that  the  air,  to  be  of  value, 
must  be  finely  comminuted,  but  that  any  addition  was  of  value  that 
would  decrease  the  energy  required  to  secure  aeration  by  means 
of  mechanical  agitation. 

MINERALS  SEPARATION  PLANT.  The  Minerals  Separation  company, 
owners  of  the  froth  patents,  purchased  the  tailing-dumps  on  the 
Central  mine,  and,  by  arrangement,  a  plant  was  designed  and  erected 
by  the  Sulphide  Corporation  for  their  treatment.  The  plant  is 
shown  in  cross-section  in  Fig.  23,  and  was  designed  on  previous 
experience  for  the  treatment  of  2000  tons  per  week.  It  was  finished 
at  a  cost  of  £26,000  complete.  The  efficiency  of  the  grinding-pans 
proved  so  great  with  the  new  design  of  positive  pan  that  the  plant 
was  able  easily  to  handle  5000  tons  per  week.  This  plant  was 
responsible  for  the  treatment  of  709,999  tons  of  tailing,  etc.,  and 
the  production  of  242,462  tons  of  concentrate  up  to  the  time  it  was 
shut-down  in  June  1911  on  the  exhaustion  of  the  dumps. 

In  connection  with  the  Minerals  Separation  plant,  it  is  important 
to  note  that  the  fact  of  the  circuit  being  no  longer  acid,  but  neutral, 
has  been  taken  advantage  of,  inasmuch  as  there  is  only  one  circuit 
through  iron  grinding-pans,  agitators,  and  spitz-boxes.  The  original 


FLOTATION   AT   THE  CENTRAL   MINE,    BROKEN   HILL 


123 


granulation  plant,  being  designed  for  an  acid  circuit,  was  equipped 
originally  with  wood  throughout  where  liquor  circulated,  and  with 
dry-crushing  ball-mills  for  the  same  reason.  Later,  wet  crushing 
was  adopted,  but  with  a  fresh-water  circuit,  kept  carefully  separate 
from  the  acid  circuit  in  which  the  actual  separation  took  place.  The 
successful  development  of  the  flotation  process,  however,  has  enabled 
both  crushing  and  separation  to  be  conducted  in  one  and  the  same 
circuit,  and  has  thus  greatly  simplified  operations. 

The  liquor  that  was  circulated  through  the  Minerals  Separation 
plant    was    approximately    25,000    gallons  per    hour.     During    the 


HALF  SECTION  THROUGH 


H*ir  SECTION  THROUGH 

riOATATIOH 


FlG.    23.      THE   PLANT    AT    THE    CENTRAL    MINE. 


course  of  operation,  therefore,  over  600,000,000  gal. — equal  to  nearly 
3,000,000  tons — has  passed  through  the  12  iron  grinding-pans  of  this 
plant  without  detrimental  effect.  No  stronger  evidence  could  be 
produced  as  to  the  freedom  of  the  circuit-liquor  from  acidity. 
The  maintenance  charges  on  these  iron  pans  are  no  heavier  than 
corresponding  charges  on  exactly  similar  grinding-pans  in  the  lead- 
mill  crusher-section,  where  fresh  water  only  is  used. 

Following  exhaustive  experiments  in  the  laboratory,  various  media 
have  from  time  to  time  been  used  for  long  periods  on  the  commercial 
scale,  both  in  substitution  for  and  in  combination  with  oleic  acid. 
Chief  among  such  media  are  amyl  alcohol,  resin-oil,  camphor-oil, 
pine-oil,  and  eucalyptus,  with  all  of  which  ingredients  good  work 
has  been  obtained.  Thus  Nature,  in  close  proximity  to  the  vast 
bodies  of  complex  ore,  has  provided  the  means  for  the  concentration 
of  such  ores,  for  the  essential  oil  of  the  Australian  eucalyptus  is  one 
of  the  best-known  media  available  for  the  successful  exploitation  of 
refractory  Australian  ores.  It  is  of  interest  to  note  here  that  this 


124 


THE  FLOTATION   PROCESS 


application  of  an  Australian  product  to  the  treatment  of  complex 
ores  is  the  outcome  of  a  research  on  the  Central  mine  by  an  Australian 
metallurgist,  Henry  Lavers;  and  it  was  also  in  the  milling-plant  on 
the  Central  mine  that  eucalyptus  oil  was  first  used  on  a  commercial 
scale  for  concentration  by  flotation. 

This  satisfactory  stage  having  been  reached,  attention  could  now 
be  turned  to  improvements  in  methods  of  handling,  and,  on  suggestions 
from  the  owners  of  the  patents,  it  was  found  that,  by  connecting  the 
bottom  of  each  spitz-box  with  the  bottom  of  the  next  mixer  in  series, 
that  all  the  spitz-boxes  could  be  kept  on  one  floor,  thus  improving 
the  supervision  of  the  work.  An  experimental  plant  of  this  nature 
was  erected  at  the  end  of  our  No.  2  zinc  section  in  September  1910, 
and,  proving  highly  successful,  the  system  was  altered  with  confidence 
to  this  method  of  working.  Experience  shows  that,  for  ideal  work, 
the  feed  material  should  all  pass  through  40-mesh,  but  it  is  impossible 
to  secure  this  condidtion  of  grinding  at  all  times  in  the  mill,  as 
designed.  Moreover,  although  the  Sulphide  Corporation  was  quite 
aware  that  improvements  in  character  of  plant  and  methods  of 
operation  generally  were  easily  possible,  their  attention,  by  force 
of  circumstances,  had  to  be  turned  sedulously  to  increasing  the 
production  with  the  appliances  at  hand.  As  illustrating  what  the 
writer  means  by  ideal  grinding,  the  records  of  the  average  assays 
of  residues  show  continually  that  where  the  average  in  zinc  is  from 
2  to  2.5%,  that  portion  remaining  on  40-mesh  will  assay  from  3  to  4% 
zinc.  As  illustrating  the  character  of  feed,  and  proving  that  the 
process  is  capable  of  handling  successfully  the  very  finest  material, 
sizing-analyses  by  commercial  screens  of  the  feed  to  the  zinc-section, 
zinc-concentrate  as  shipped,  and  de-leading  plant  lead-concentrate 
as  shipped,  are  given : 


Feed  to 

zinc  section. 

Zinc  concentrate. 

De-leading 

lead. 

Through 

On               % 

Through     On 

% 

Through     On 

% 

40            11.2 

40 

1.5 

40 

1.9 

40 

60            21.4 

40              60 

16.9 

40               60 

7.5 

60 

80            19.4 

40               80 

21.1 

60               80 

15.8 

80 

130            15.6 

80            130 

21.7 

80             130 

18.8 

130 

180              7.3 

130            180 

7.4 

130            180 

8.5 

180 

25.0 

180 

31.4 

180 

47.5 

RESULTS  OBTAINED.  For  comparison  with  the  work  of  the  old 
mill,  the  following  summary  of  results  achieved  by  the  existing  plant 
will  be  of  interest.  This  table  summarizes  work  done  on  a  commercial 
scale  in  the  Central  mill  over  a  period  of  twelve  months,  ending 


FLOTATION  AT   THE  CENTRAL   MINE,    BROKEN   HILL  125 

December  28,  1912,  and  demonstrates  conclusively  the  vast  improve- 
ment in  concentration  practice  made  possible  by  the  adoption  of 
the  flotation  process. 

SUMMARY 

, Assay  value. >,      ,-- Recoveries.  ^ 

Prop.,     Ag,        Pb,       Zn,      Ag,       Pb.      Zn, 

Lead  concentrate  ex  lead  section...  16.0  33.1  67.0  6.7  44.7  72.4  6.1 
Lead  concentrate  ex  de-lead  plant..  1.4  50.9  62.5  12.5  5.9  5.8  1.0 


Total   lead  concentrate 17.4      34.5      66.7        7.1      50.6      78.2        7.1 

Zinc  concentrate    32.7      16.1        8.1      46.4      42.1      15.9      84.7 

Total   concentrates    50.1     92.7     94.1     91.8 

Modifications  of  the  wet  mill  are  now  in  hand  for  the  improvement 
of  the  grinding,  but  it  is  felt  that,  as  the  proportion  of  lower-level 
ore  increases,  the  grinding  appliances  will  have  to  be  increased  in 
order  to  allow  for  the  finer  crystallization  of  the  minerals  in  the  ore 
as  further  depth  is  attained.  The  writer  is  of  opinion  that  the  figures 
quoted  clearly  show  that  if  the  ideal  grinding  is  obtained  the  already 
high  recoveries  of  metals  will  be  further  augmented. 

It  is  unique  in  the  history  of  concentration  that  so  far-reaching 
and  extensive  a  development  should  have  reached  its  present  state 
of  perfection  in  so  short  a  space  of  time,  and  more  wonderful  still 
that  it  should  prove  applicable  in  an  equally  masterly  manner  to 
so  many  other  classes  of  ore.  There  can  be  little  doubt  left  in  the 
minds  of  those  who  have  seen  this  new  system  of  concentration  that 
it  must  of  necessity  spread  to  all  parts  of  the  world. 


126  THE  FLOTATION  PROCESS 

WHAT   IS   FLOTATION? 

By  T.  A.  RICKARD 
(From  the  Mining  and  Scientific  Press  of  September  11,  1915) 

Flotation,  in  its  latest  phase,  is  a  process  of  concentrating  ores 
by  frothing.  When  crushed  ore,  previously  mixed  with  water  and 
a  relatively  minute  addition  of  oil,  is  agitated  violently  in  the 
presence  of  air,  a  froth  is  formed.  This  froth,  rising  to  the  surface 
of  the  liquid  mixture,  is  laden  with  sulphides  or  other  metallic 
particles,  while  the  earthy  material,  or  gangue,  subsides  to  the 
bottom.  The  froth  is  " thick,  coherent,  and  persistent/'* 

The  formation  of  this  froth  depends  upon  a  number  of  physical 
causes,  of  which  the  buoyancy  of  oil  is  the  one  most  generally 
associated  with  the  flotation  process.  Surface  tension,  however,  is 
the  phenomenon  to  be  considered  first.  Then  viscosity. 

Every  millman  has  had  occasion  to  notice  how  sulphides  are 
carried  on  the  surface  of  wash- water  in  a  stamp-mill;  for  example, 
when  water  is  passed  over  the  dry  surface  of  an  amalgamating-table 
or  a  vanner-belt.  The  metallic  particles  are  dry  and  to  their  surfaces 
is  attached  a  film  of  air  that  buoys  them  on  the  water.  To  a  similar 
cause  is  due  the  loss  of  ' float  gold'  in  tailing.  Most  of  us  learned 
early  that  grease  of  any  kind  was  bad  for  amalgamation.  It  'sickens' 
the  quicksilver,  coating  the  globules  so  that  they  do  not  coalesce  but 
remain  in  a  'floured'  or  minutely  globular  condition.  This  may 
account  for  the  loss  of  quicksilver,  but  the  further  loss  of  gold  must 
be  imputed  to  the  fact  that  the  fine  scaly  bright  gold  attaches  itself 
readily  to  the  oiled  spheres  of  mercury  and  is  carried  with  them 
into  the  creek. 

The  surface  of  any  liquid  behaves  as  if  it  had  a  film  or  elastic 
skin.  To  this  fact  is  due  the  variation  in  the  maximum  size  of 
drops  of  different  liquids.  As  the  drop  enlarges,  the  strength  of 
this  skin  is  exceeded;  then  the  drop  breaks  and  the  liquid  falls. 
"When  an  iron  ring  is  dipped  into  a  solution  of  soap,  it  will  be  seen, 
on  taking  it  out,  that  a  film  of  the  liquid  stretches  across  the  ring. 
If  a  small  loop  of  cotton,  previously  moistened  with  the  solution, 
is  placed  on  the  film  left  on  the  ring,  this  loop  can  be  made  to 
assume,  and  retain,  any  form,  such  as  is  shown  at  A  in  Fig.  24.  If, 


"That  is  the  description  given  by  the  Minerals  Separation  metallurgists, 
it  is  a  description  denied  by  others,  more  particularly  those  using  the  Callow 
machine. 


WHAT    IS    FLOTATION? 


127 


however,  the  film  within  the  loop  is  broken,  the  loop  immediately 
assumes  the  circular  form,  shown  at  B;  and  if  it  is  now  deformed 
in  any  way,  on  being  released  it  springs  back  at  once  to  a  circle. 


FIG.  24. 

These  phenomena  indicate  that 'the  particles  at  the  surface  of  a 
liquid  have  a  greater  coherence  than  the  particles  in  the  interior 
of  the  liquid.  The  force  that  does  this  is  surface  tension.  The 
experiment  with  the  ring  and  the  loop,  for  example,  is  explained 
by  the  fact  that,  in  the  first  place,  "the  surface  tension  of  the 
liquid  acts  equally  on  both  sides  of  the  cotton,  but  when  the  film 
inside  the  loop  is  broken,  the  surface  tension  only  acts  on  one  side,, 
and  hence  draws  the  loop  out  into  a  circle. '  'f 

Surface  tension  can  be  measured.    A  framework1  (Fig.  25)  consist- 

A  C  E         B 


G-  X 

FIG.    25.      ARRANGEMENT   FOR    MEASURING    STRENGTH    OF    FILM. 


t'A  Text-Book  of  Physics,'  by  W.  Watson,  page  191. 

i'A  Text  Book  of  the  Principles  of  Physics/  by  Alfred  Danniell,  1911. 


128  THE  FLOTATION  PROCESS 

ing  of  a  transverse  bar  A  B,  and  two  grooved  slips  C  D  and  E  F, 
will  allow  the  piece  of  wire  G  H  I  J  to  slip  freely  up  and  down.  The 
wire  H  I  is  pushed  against  A  B  and  a  quantity  of  the  liquid  is 
applied  between  them.  The  little  pan  X  is  loaded  with  sand  until 
the  wire  H  I  is  pulled  from  A  B.  The  minimum  force  required  to 
do  this  is  mg,  the  weight  of  m  grams.  This  weight  suspended  on  the 
film  equals  the  tension  of  the  film  on  the  wire.  If  the  film  stretches 
until  the  wire  H  I  is  at  p,  then  the  film  has  an  area  C  E.Cp.  The 
total  weight  mg  is  distributed  over  the  breadth  C  E-  whence,  if  T 
represents  the  superficial  tension  across  the  unit  of  length  C  E, 
thenm<7  =T.CEorT=^ 

Thus  the  force  of  surface  tension  between  water  and  air  has  been 
determined ;  it  is  3  J  grams  per  linear  inch  or  81  dynes*  per  centimetre, 
which  being  interpreted  means  that  40  grains  would  be  supported 
by  a  film  one  foot  long. 

The  surface  tension  of  various  liquids  is  as  follows : 

Tension  of  surface  sep- 
arating the  liquid  from 
Liquid.  .  Sp.  Gr.  Air.  Water. 

Water    1.00  81 

Mercury    13.54  540  418 

Alcohol    0.79  25.5  

Olive  oil    0.91  36.9  20  56 

Turpentine    0.88  29.7  11.55 

Petroleum    0.79  31.7  27.8 

These  are  given  in  dynes  per  centimetre  as  determined  by  Quincke, 
and  recorded  in  the  Encyclopedia  Britannica.  However,  a  liquid 
has  another  characteristic  that  must  not  be  overlooked,  namely, 
viscosity  or  resistance  to  flow.  This  gives  toughness  to  the  superficial 
film.  Water-spiders  will  run  over  the  surface  of  a  pool  like  boys 
on  skates  over  thin  ice.  The  spider's  feet  do  not  break  through, 
although  each  tread  makes  a  dimple  on  the  surface.  H.  H.  Dixon 
actually  measured  the  pressure  exerted  by  the  spider's  feet  on  the 
water.  He  photographed  the  shadow  of  the  dimple  and  then  mounted 
one  of  the  spider's  feet  on  a  delicate  balance  and  made  it  press  on 
the  water  until  it  made  a  dimple  of  the  same  depth  as  that  previously 
observed. 

The   next  phase   of  the   subject  is  illustrated   by   the   familiar 


*See  also  page  11  of  this  book. 


WHAT    IS   FLOTATION?  129 

experiment  with  a  greased  needle.  If  you  place  an  ordinary  needle, 
say,  a  lace  needle  suitable  for  use  with  No.  80  thread,  on  the  surface 
of  a  bowl  of  water,  it  sinks  at  once  to  the  bottom,  in  obedience  to 
the  law  of  gravity,  f  If,  however,  you  pass  the  needle  through  your 
hair,2  so  that  it  becomes  greased,  it  will  float  on  the  water.  Why 
the  difference  of  behavior?  In  its  ordinary  state  the  needle  has  a 
film  of  air  attached  to  it.  That  film,  being  loosely  held,  is  readily 
displaced  by  the  water,  so  that  the  needle  becomes  wetted,  that  is, 
its  weight  causes  it  to  break  through  the  elastic  skin  constituting 
the  surface  of  the  water.  On  the  other  hand,  when  the  needle  is 
greased,  the  film  of  air  around  it  is  displaced  by  a  film  of  oil,  which 
is  firmly  held,  because  lustrous  metallic  surfaces  have  a  selective 
adhesion  for  oil.  Moreover,  gases  have  a  marked  adhesiveness  for 
oils,  so  that  air  adheres  readily  to  the  film  of  oil  on  the  needle.  On 
account  of  this  envelope  of  oil  and  air,  the  needle  is  not  wetted, 
that  is,  it  fails  to  rupture  the  surface.  The  needle  lies  in  a  depression 
in  the  surface  of  the  water,  but  the  amount  of  displacement  does 
not  account  for  the  floating.  Viscosity,  however,  may  play  a  part, 
by  increasing  the  tenacity  of  the  film,  the  particles  of  which  are  so 
held  together,  or  cohere,  that  the  needle  fails  to  part  them.  In  short, 
although  it  is  eight  times  heavier  than  water,  the  steel  floats. 

Another  suggestive  experiment  is  that  of  the  grapes  in  soda-water. 
Fill  a  glass  two-thirds  full  with  soda-water  from  an  ordinary  'syphon' 
and  then  drop  two  or  three  small  grapes  into  it.  The  grapes  sink 
to  the  bottom,  but  they  become  restless  almost  immediately  and  soon 
rise  to  the  surface,  one  after  the  other.  They  do  not  remain  there; 
first  one  and  then  the  other  sinks.  This  performance  will  continue 
for  half  an  hour,  the  individual  grapes  rising  and  falling,  not  always 
the  whole  way,  but  maintaining  a  condition  of  intermittent  activity. 
They  become  quiet  only  when  bubbles  cease  to  be  generated  at  the 
bottom,  that  is,  when  the  carbonic-acid  gas  has  been  driven  out  of 
the  water  by  the  relief  of  pressure.  By  watching,  it  is  seen  that 
the  bubbles  attach  themselves  to  the  grapes  and  buoy  them  to  the 
surface,  where  the  bubbles  break.  Sometimes  a  couple  of  grapes  will 
collide  and  cause  the  adhering  bubbles  to  become  detached,  so  that 
one  or  both  of  the  grapes  sink.  In  the  end  the  bubbles  become  too 
few  to  buoy  the  grapes,  so  that  the  latter  rise  only  part  of  the  way ; 
finally,  they  lie  motionless  at  the  bottom.  During  the  early  and 


tSee  also  pp.  327  and  356  of  this  book. 
2(Dr  even  through  your  fingers. 


130  THE  FLOTATION  PROCESS 

active  part  of  the  performance,  the  grape  will  strike  the  surface  of 
the  water  and  rebound  from  it  as  if  it  were  a  membrane. 

The  buoyancy  of  oil  is  the  physical  fact  most  associated  with 
the  first  development  of  flotation,  although  it  is  subordinated  in  the 
latter  phases  of  the  process.  Oil  has  a  specific  gravity  less  than  that 
of  water,  and  therefore  rises  to  the  surface  when  mixed  with  water. 
The  lighter  oils  range  in  specific  gravity  from  0.8  to  0.95,  as  against 
the  1.0  of  water,  so  that  the  margin  for  buoying  particles  heavier 
than  water  is  small.  For  instance,  to  make  a  mixture  of  zinc  sulphide 
and  oil  as  light  as  water,  it  would  be  necessary,  even  with  the  lighter 
oils,  to  use  from  3  to  15  times  as  much  oil  by  weight  as  the  blende. 
This  suggests  that  flotation,  even  as  conducted  on  the  lines  of  the 
older  patented  processes,  cannot  be  due  entirely  to  the  buoyancy 
of  oil. 

The  selective  adhesion  of  oil  for  particles  having  a  metallic 
lustre  is  a  decisive  factor  in  the  process.  It  has  been  said  that 
this  adhesiveness  is  characteristic  of  sulphides;  but  it  is  exhibited 
by  tellurides  and  by  graphite  also.  Similarly,  it  has  been  imputed 
to  'mineral'  and  to  'metallic'3  particles,  but  both  terms  would  include 
substances  outside  the  range  of  this  phenomenon.  Apparently  it  is 
the  metallic  lustre  that  is  the  decisive  factor,  for  this  would 
include  the  minerals  especially  amenable,  such  as  molybdenite, 
graphite,  the  tellurides,  and  the  bright  sulphides.  The  effect  of  this 
marked  preference  of  oil  for  lustrous  metallic  surfaces  is  intensified 
by  the  fact  that  gases  (such  as  air)  have  a  similar  adhesiveness  for 
oil,  so  that,  if  present  in  water,  they  will  join  in  preventing  the 
wetting  of  the  metallic  surfaces.  It  is  an  equally  important  fact 
that  quartz  and  other  gangue-minerals,  having  a  'non-metallic'  as 
against  a  'metallic'  lustre,  exhibit  the  opposite  preference:  they  are 
feebly  adhesive  to  films  of  oil,  and  therefore  to  those  of  gas,  while 
they  are  strongly  adhesive  to  water,  that  is,  they  are  easily  wetted. 
The  reason  for  this  difference  is  not  known;  it  may  belong  to  the, 
as  yet,  mysterious  realm  of  electro-statics,  but  it  is  a  fact  that  the 
curve  of  contact,  or  wall-angle,  between  metallic  particles  and  water 
is  convex  while  that  between  earthy  particles  is  concave. 

Whatever  the  reason  for  this  difference,  it  can  be  accentuated  by 


s'Metallic,'  in  this  context  may  mean  minerals  with  a  metallic  lustre, 
including  graphite,  and  'mineral'  may  be  meant  in  the  sense  of  ore,  the 
valuable  part  of  the  vein  or  lode,  as  distinguished  from  the  worthless  earthy 
matter  or  gangue.  In  French,  mineral  means  'ore.'  Sometimes  'sulphide'  is 
preferred,  but  that  excludes  the  tellurides  and  graphite.  At  least  one  sulphide 
without  metallic  lustre  is  readily  amenable  to  notation,  namely,  cinnabar. 


WHAT    IS   FLOTATION?  131 

acidulation  of  the  water.  "Acidified  water  has  a  greater  wetting 
power  than  neutral  water."  For  this  fact  also  no  satisfactory  expla- 
nation is  forthcoming.  In  some  cases,  the  acid  may  be  supposed  to 
dissolve  any  coating  of  oxide  on  the  metallic  surface,  rendering  it 
more  lustrous,  while  on  the  other  hand,  the  acidity  of  the  water  may 
give  it  a  corrosive  penetration  beneath  the  surface  of  the  gangue. 

The  addition  of  acid  in  quantity  produces  another  effect,  namely, 
effervescence  or  the  liberation  of  carbonic-acid  gas  by  the  reaction 
with  calcite,  rhodochrosite,  or  other  carbonates  such  as  are 
often  present  in  the  ore.  This  generates  bubbles  that  will  buoy 
the  metallic  particles,  whether  oiled  or  not.  But  water  contains  air 
in  solution;  hence  by  heating  the  water,  or  by  diminishing  the 
pressure,  it  is  possible  to  release  the  air  in  the  form  of  bubbles  that 
attach  themselves  to  the  metallic  particles,  like  the  bladders  used  by 
persons  learning  to  swim.  Moreover,  by  a  violent  agitation  of  the 
mixture  of  ore,  water,  and  oil  (if  added)  it  becomes  easy  to  entrain 
or  entangle  a  large  volume  of  air,  which  will  rise  through  the  mass 
in  the  form  of  myriad  bubbles,  constituting  a  foam  or  froth  of 
varying  strength  and  persistence. 

Oil  reduces  the  surface  tension  of  water,  that  is,  between  water 
and  air.  Pure  water  has  great  surface  tension,  it  also  has  no  super- 
ficial viscosity;  that  is  why  it  will  not  froth.  The  addition  of  oil 
lowers  the  surface  tension  and  imparts  a  decided  viscosity  to  the 
surface  of  the  water.  That  is  why  the  pouring  of  oil  on  troubled 
waters  abates  their  turbulence.  That  also  explains  why  the  placing 
of  oil  in  stagnant  pools  kills  the  larvae  of  tlra  mosquito,  which  then 
finds  it  impossible  to  adhere  to  the  surface  by  their  breathing-tubes. 
(See  Fig.  26.) 


FIG.    26.      LARVAE   OF   THE    MOSQUITO   ATTACHED   TO    SURFACE   OF   WATER. 


132  THE  FLOTATION  PROCESS 

Consider  the  beautiful  soap-bubble.  The  oil  of  the  soap  is  an 
impurity  that  lowers  the  surface  tension  of  the  water;  by  stretching 
of  the  film  of  the  bubble  this  effect  is  diminished  through  the  dilution 
of  the  impurity,  making  the  film  stronger  and  less  prone  to  collapse.4 
Thus  it  renders  the  bubble  more  persistent.  The  bubble  therefore  is 
another  illustration  of  surface  tension,  for  it  is  an  elastic  skin  of 
water  enclosing  gas,  like  a  balloon.  Here  also  the  property  of  viscosity 
comes  into  play,  for  the  addition  of  oil  to  the  water,  more  particularly 
after  exposure  to  the  air,  as  in  agitation,  gives  tenacity  to  the  super- 
ficial film.  The  combination  of  low  tension  and  high  viscosity  enables 
a  bubble,  rising  through  the  liquid,  to  envelop  itself  in  the  surface  film 
of  the  liquid,  which  the  tension  of  the  bubble-film  is  not  strong 
enough  to  break,  so  that  the  bubble  endures.5  The  noise  made  by  the 
bursting  of  a  bubble  suggests  the  fact  that  it  is  a  receptacle  of  energy.* 

The  bubble  is  spherical  because  the  sphere  is  the  shape  involving 
the  smallest  surface  or  superficial  area.  The  bubble  has  an  affinity 
for  the  lustrous  metallic  particles  and  adheres  to  them,  as  it  also 
adheres  to  the  smooth  sides  of  a  glass.  This  particle  of  air,  or  other 
gas,  is  enveloped  in  an  elastic  skin  of  the  contaminated  viscous  liquid 
in  which  it  has  been  generated  and  the  metallic  particles  do  not  break 
through  that  skin  for  the  same  reason  as  the  greased  needle  failed  to 
be  drowned  in  the  water. 

The  addition  of  soluble  oils  assists  the  formation  of  bubbles  in 
the  mass  of  ore  and  water.  These  three  constituents  of  the  flotation 
pulp  are  mixed  intimately  so  as  to  form  an  'emulsion/  such  as  is 
typified  by  mayonnaise.  The  air  present  while  the  emulsion  is  being 
made  furnishes  the  gas  for  the  bubbles.  In  order  that  they  may  lift 
the  metallic  particles,  they  must  endure  long  enough  to  permit 
complete  separation  of  the  metallic  particles  from  the  earthy  particles, 
that  is,  the  sorting  of  the  valuable  from  the  non-valuable  components 
of  the  ore.  For  the  purpose  of  metallurgical  concentration  the  rate 
at  which  the  bubbles  burst  must  be  slower  than  that  at  which  they 
are  being  formed.  An  effective  froth  represents  a  multiplicity  of 
persistent  bubbles.  The  relative  stability  of  the  bubbles  depends  also 
upon  the  kind  of  oil  employed.  Pine-oil  makes  a  brittle  film ;  creosote 
yields  an  elastic  envelope. 

By  a  wonderful  correlation  of  physical  forces,  the  metallic  par- 
ticles become  attached  to  the  bubble,  made  in  the  metallurgical  emul- 


4C.  V.  Boys,  'Soap  Bubbles,'  page  105. 
sDanniell,  Op.  cit..  page  278. 
*See  also  page  311  of  this  book. 


WHAT   IS   FLOTATION?  133 

sion,  in  such  a  way  as  to  serve  as  a  protective  armor,  the  particles  of 
varying  size  interlocking  on  its  spherical  envelope.  The  bubbles 
without  mineral  are  like  a  balloon  with  a  weak  gas-bag,  which  is 
likely  to  burst,  while  the  armored  bubbles  are  like  a  balloon  with  a 
strong  gas-bag,  which  does  not  burst.  Variety  of  size  among  the 
metallic  particles  favors  the  construction  of  the  interlocking  mineral 
coat  on  the  bubble,  just  as  materials  of  various  size  help  to  make  a 
dense  concrete.  Hence  slime  is  no  hindrance. 

Intimate  mixing  is  required.  The  more  thorough  the  mixing,  the 
cleaner  the  separation  of  the  metallic  from  the  earthy  particles.  This 
is  said  to  be  due  to  the  complete  oiling  of  the  metallic  particles,  but 
it  is  a  fact  that  no  oil  can  be  discerned  on  the  concentrate  when  using 
the  J  to  -J  pound  of  oil  per  ton  sufficient  in  most  cases  for  the 
purpose  of  the  process.  The  mixing  may  be  beneficial  for  reasons 
other  than  the  oiling  of  the  concentratable  parts  of  the  ore;  it  may 
cause  enough  friction  to  clean  the  metallic  surface;  it  may  promote 
such  a  solution  of  the  oil  in  the  water  as  ensures  the  formation  of 
the  right  kind  of  bubbles  for  a  mineral-carrying  froth.  Heat,  by  the 
injection  of  steam,  increases  the  miscibility,  or  ability  to  be  mixed, 
of  the  oil,  thinning  it  so  that  it  will  extend  over  a  larger  surface,  as 
butter  is  warmed  to  make  it  spread  over  pop-corn.  Many  common 
oils,  such  as  'red  oil*  and  other  forms  of  oleic  acid,  are  solid  at  the 
ordinary  temperature,  so  that  heat  sufficient  to  raise  the  temperature 
of  the  emulsified  pulp  to  about  80°  F.  is  desirable. 

To  apply  this  process  of  concentration,  the  ore  is  crushed  to 
the  degree  of  firmness  required  to  separate  the  metallic  minerals  from 
the  earthy  gangue.  This  may  mean  anything  from  40  to  200-mesh. 
The  crushed  ore  is  then  mixed  with  water  in  the  ratio,  say,  of  3:1, 
although  theoretically  2  : 1  would  make  a  better  emulsion ;  oil  is 
added,  say,  in  the  proportion  of  J  Ib.  per  ton  of  ore;  and  the 
mixture  is  agitated  violently  in  the  presence  of  air,  by  paddles 
or  beaters,  by  passage  through  a  centrifugal  pump,  or  by  jets  of 
compressed  air.  Acid  is  not  necessary,  as  we  now  know,6,  although 
it  has  heretofore  been  considered  requisite.  Whether  oil  is  absolutely 
essential  is  open  to  doubt.  Agitation  of  the  pulp  in  the  presence  of 
air  is  the  prime  factor  in  producing  the  desideratum,  namely  froth. 
What  machines  are  best  adapted  to  ensure  proper  agitation  is  a 
matter  for  separate  consideration.  Aeration  of  a  liquid  by  agitation 


e'Flotation  in  a  Mexican  Mill,'  Mining  and  Scientific  Press,  July  24,  1915, 
page  123.  Also  Charles  Butters,  M.  &  S.  P.,  August  21,  1915.  See  pages  93 
and  120  of  this  book. 


134  THE  FLOTATION  PROCESS 

in  the  presence  of  air  and  forcing  of  the  air  into  it  so  as  to  form 
multitudinous  small  bubbles,  producing  a  froth,  is  done  every  day 
in  the  domestic  operations  of  the  beating  of  eggs  and  the  whipping 
of  cream. 

We  have  now  got  our  froth.  This,  as  it  accumulates  on  the 
surface  of  the  emulsified  pulp,  may  be  from  2  to  3  inches  up  to 
10  or  15  inches  thick.  It  is  so  densely  coated  with  the  sulphides  as 
to  be  black,  while  the  gangue  that  falls  to  the  bottom  is  so  clean 
as  to  be  white.  By  skimming,  using  radial  arms  or  scrapers,  or  a 
simple  flow,  the  froth  is  removed  to  a  secondary  receptacle  or  'cell,' 
of  the  spitzkasten  or  V-shaped  type,  where  it  is  cleaned  by  a  repetition 
of  the  process,  making  a  high-grade  concentrate,  while  the  discard 
goes  back  for  re-treatment.  In  short,  all  that  is  needed  is  some 
arrangement  for  thorough  mixing  and  aeration,  by  the  use  of  paddles 
or  air  under  pressure;  then  the  removal  of  the  resulting  froth  so 
that  the  floated  mineral  will  not  drop  when  the  bubbles  break.  When 
the  froth  has  been  collected,  it  is  filtered,  yielding  a  cake  containing 
about  10%  moisture,  which  may  be  dried  before  shipment  or  final 
treatment  for  the  extraction  of  the  precious  metals. 


WHY  IS  FLOTATION?  135 

WHY  IS  FLOTATION? 

By  CHARLES  T.  DURELL 
(From  the  Mining  and  Scientific  Press  of  September  18,  1915) 

Some  of  the  fundamental  principles  of  this  concentration  'upside 
down,'  as  it  may  be  termed,  being  such  a  new  method,  have  been 
overlooked.  There  has  been  such  a  mad  scramble  to  get  results  in 
advance  of  the  'other  fellow/  and  to  penetrate  the  cloud  of  secrecy 
enforced  by  patent  litigation,  that  there  has  been  little  time  to  answer 
the  question  as  to  why  the  heavier  mineral  floats  and  the  lighter 
gangue  sinks.  In  this  buzzing  cloud  of  secrecy  the  student  can 
distinguish  such  phrases  as  'froth  flotation/  'surface  tension/  'oil- 
films/  'DeBavay  float/  'liquid  skins/  etc.,  all  of  which  tend  to 
confuse  rather  than  answer  the  main  question.  A  few  articles  in 
the  magazines  have  given  various  data,  phenomena,  causes,  and 
effects,  but  no  definite  theory  explaining  these  has  been  clearly  stated. 

The  action  of  any  flotation  machine  in  successful  operation  seems 
quite  simple,  the  mineral  floating  in  preference  to  the  gangue,  giving 
rise  to  the  phrase  'selective  flotation.'  All  that  is  necessary  for 
the  one  type  of  machines  is  to  place  the  mineral  particles  gently 
on  the  surface  of  a  liquid  so  that  they  will  not  sink  or,  in  the  other 
type  of  machines,  attach  to  them  something  of  a  lighter  specific 
gravity  than  the  liquid  so  that  they  will  rise  bodily  to  the  surface. 
On  the  face  of  it,  this  is  quite  simple.  Apparently  the  simplest 
of  all  is  to  attach  'life-preservers'  or  something  buoyant  to  the  mineral 
particles. 

Herodotus  describes  how  "the  virgins  drew  up  gold  by  means 
of  feathers  daubed  in  pitch. ' '  Therefore  this  or  an  oil,  for  instance, 
can  be  employed  to  float  mineral.  The  Elmore  patents  for  this 
flotation,  due  to  the  buoyant  property  of  oil,  are  still  in  effect.  Owing 
to  the  large  quantity  of  oil  necessary,  as  well  as  other  things  that 
make  this  method  of  no  commercial  value  at  present,  the  only  'why' 
to  be  considered  in  this  class  of  flotation  is  the  selective  action,  which 
will  be  discussed  later. 

The  simplest  and  cheapest  'life-preserver'  is  undoubtedly  the 
pneumatic  one,  which  is  beyond  the  time  of  Herodotus  or  perhaps 
even  history  itself,  since  eggs  and  cream  were  surely  frothed  before 
the  stylus  was  known.  Any  little  girl  who  has  helped  her  mother 
in  the  kitchen  can  tell  how  any  foreign  substance,  such  as  a  piece  of 
egg-shell  for  instance,  is  buoyed  up  and  brought  to  the  surface  by 


136  THE  FLOTATION  PROCESS 

these  bubbles.  These  are  bubbles  of  air,  and  what  could  be  cheaper 
for  the  manufacture  of  these  simple  pneumatic  *  life-preservers'? 
It  is  true  that  Delprat,  with  his  process,  uses  carbon  dioxide,  but  this 
is  simply  a  case  of  using  a  by-product  that  would  otherwise  go  to 
waste. 

Therefore  the  whole  sum  and  substance  of  this  apparently  complex 
problem  of  ore  concentration  by  flotation,  now  surrounded  by  a 
cloud  of  secrecy,  consists  in  either  attaching  mineral  particles  to 
gas  bubbles,  preferably  air,  or  attaching  air  bubbles  to  mineral 
particles.  It  amounts  to  the  same  thing  whether  the  bubble  be 
attached  to  the  solid  or  the  solid  attached  to  the  bubble.  In  the 
one  case,  'surface  tension'  type  of  machine  is  used  for  the  concen- 
tration, while  in  the  other  a  ' froth'  type  of  machine  is  used.  These 
will  be  taken  up  later. 

Therefore  the  two  prime  requisites  to  flotation  are: 

1.  Attachment  of  bubbles  to  solids; 

2.  Creation  of  selective  action  of  bubbles  for  metallic  particles 
instead  of  for  the  gangue  particles. 

Since  the  all-important  requisite  is  the  attachment  of  gas  bubbles 
to  solids,  it  is  logical  to  investigate  this  phenomenon  first  with  the 
simplest  material  at  hand — air  and  water. 

Far  back  in  primeval  time  the  progenitors  of  the  fishes  made 
air  bubbles  that  came  to  the  surface  of  the  water  and  yet  we,  a 
few  years  ago,  knew  but  little  more  concerning  air  bubbles  in  water. 
There  was  no  reason  for  these  aquatic  things  knowing  the  ways 
that  air  can  exist  in  water  but  there  was  no  excuse  for  our  building 
Pachuca  tanks,  blowing  air  in  at  the  bottom  and  then  writing  a 
beautiful  chemical  equation  to  show  that  these  air  bubbles  were 
necessary  for  dissolving  gold.  Visible  bubbles  of  air,  which  have 
been  blown  into  the  water,  can  in  no  possible  way  sustain  the  life 
of  a  fish.  Neither  can  they  aid  one  iota  in  dissolving  gold  in  a  cyanide 
solution.  Nor  can  visible  bubbles  of  air,  introduced  into  a  liquid 
in  this  way,  be  attached  to  solids  to  aid  in  flotation.  Available  air 
or  oxygen  for  things  of  this  nature  must  be  air  actually  in  solution. 
A  fish  may  be  breathing  freely  at  the  bottom  of  an  aquarium.  If 
the  water  be  warmed  so  as  to  expel  the  air,  the  fish  will  rise  to 
the  surface  and  try  to  jump  out.  Only  nascent  hydrogen  can  unite 
with  arsenic  in  the  Marsh  test.  In  the  same  way,  only  nascent  oxygen 
from  the  dissolved  air  can  act  as  shown  in  the  chemical  equation : 

2  Au+4  K(CN)+H2O+0=2  KAu(CN)2+2KOH. 
when  gold  is  dissolved.    Only  nascent  gas  can  be  attached  to  mineral 


WHY  IS  FLOTATION?  137 

in  the  flotation  process.  This  fact  is  quickly  demonstrated  by  intro- 
ducing a  small  jet  of  air  into  the  bottom  of  a  flask,  filled  with  water, 
where  rests  some  pulverized  ore,  the  metallic  particles  of  which  are 
in  a  perfect  float  condition.  Why  will  the  mineral  particles,  which 
almost  float  of  their  own  accord,  refuse  to  attach  themselves  or  be 
attached  to  the  small  bubbles  of  air?  To  prove  that  these  same 
metallic  particles  can  be  floated  by  bubbles  of  air,  it  is  only  necessary 
to  remove  the  jet  and  place  the  flask  on  a  hot  plate  when  they  will 
immediately  collect  air  driven  out  of  solution  by  the  heat  and  rise 
to  the  surface.  Some  one  may  here  remark,  that  the  rise  of  tempera- 
ture of  the  solution  causes  enough  expansion  of  the  air  bubbles 
already  attached  to  the  metallic  particles  to  produce  flotation. 
Anyone  familiar  with  the  law  of  Henry  will  know  this  is  not  the 
case  on  noting  the  greatly  increased  size  of  the  bubbles.  Why, 
then,  cannot  air  bubbles  be  attached  to  mineral  particles  in  the  place 
of  nascent  or  dissolved  air  ? 

All  great  facts,  when  thoroughly  understood,  are  demonstrable 
by  simple  experiments  with  material  at  hand.  Sometimes  when  the 
young  man  at  the  soda  fountain  absent-mindedly  forgets  to  stir  your 
cherry  phosphate  and  sets  before  you  the  straws,  demonstrate  the 
above  fact  to  your  satisfaction  while  the  nascent  bubbles  of  C02  form 
and  rise  to  the  surface  of  the  liquid.  Crush  the  straw  slightly  to 
reduce  the  size  so  that  only  a-  minimum  of  air  can  be  forced  through. 
With  this  straw,  blow  air  into  the  colored  syrup  in  the  bottom  of 
the  glass  so  as  to  form  a  few  small  bubbles  that  can  be  watched 
closely.  These  bubbles  that  come  to  the  surface  are  colored.  Why? 
The  air  itself  is  not  colored.  Therefore,  since  the  only  part  of  the 
liquid  that  is  colored,  is  in  the  bottom  of  the  glass,  the  air  must  be 
enveloped  in  the  same  identical  portion  of  liquid  throughout  its 
passage  from  the  bottom  to  the  top  of  the  glass.*  In  other  words, 
the  air  bubble,  on  being  introduced  into  the  liquid,  is  immediately 
surrounded  and  inclosed  by  a  film  of  liquid,  which  remains  with 
that  air  bubble  throughout  its  passage  just  as  if  it  were  a  part  of 
the  bubble.  Here  is  a  concrete  example  of  surface  tension,  a  force 
that  can  be  measured,  as  explained  in  any  text-book  of  physics. 

This  phenomenon  is  worthy  of  investigation.  The  bubble  rises 
to  the  surface  of  the  liquid  by  reason  of  the  force  of  gravity.  That 
is,  the  force  of  gravity  is  greater  than  adhesion  of  the  molecules  of 
the  air  for  the  molecules  of  the  liquid;  otherwise  the  air  would 
remain  in  the  liquid.  The  molecules  of  the  liquid  move  freely 


*See  also  pages  316  and  357  of  this  book. 


138  THE  FLOTATION  PROCESS 

among  themselves  according  to  the  definition  of  a  liquid.  In  other 
words,  the  force  of  cohesion  of  any  single  molecule  within  the  liquid 
is  equalized  by  the  cohesive  force  of  other  molecules  of  the  liquid. 
An  extraneous  force  would  be  required  to  separate  them.  An  air 
bubble,  for  instance,  introduced  into  the  liquid,  unbalances  this 
cohesive  force.  It  is  self-evident  that  this  force  of  a  molecule  must 
act  equally  in  all  directions  from  that  molecule.  Therefore  molecules 
of  the  liquid  adjacent  to  the  air  bubble  have  their  force  of  cohesion 
on  the  one  side  satisfied  by  that  of  adjacent  molecules  of  the  liquid ; 
while,  on  the  side  of  the  air  bubble,  there  are  no  molecules  of  the 
liquid  to  equalize  this  force.  Being  statical,  this  force  must  be 
equalized  by  that  of  adjacent  like  molecules  in  a  transverse  direction. 
Since  a  force  of  cohesion  was  already  in  existence  between  these 
adjacent  molecules  this  force  is  thereby  multiplied  so  that  there  then 
exists  a  greater  cohesive  force  between  the  molecules  immediately 
surrounding  the  air  bubble  than  that  existing  between  the  molecules 
in  the  interior  of  the  liquid.  This  force  is  'surface  tension;'  it  is 
so  great  that  these  molecules  of  the  liquid  surrounding  the  air  bubble 
are  firmly  held  together  and  torn  loose  from  adjacent  molecules  of 
the  liquid  as  the  bubble  rises  to  the  surface.  That  is  to  say  surface 
tension  causes  the  molecules  of  the  liquid  to  form  a  film  around  the 
bubble  and  remain  with  it  to  the  exclusion  of  like  molecules  during 
the  time  the  bubble  remains  in  the  liquid.  To  all  intents  and  pur- 
poses, this  film  is  seen  to  be  the  same  as  if  it  were  a  membrane  of 
some  solid.  The  air  in  these  bubbles  can  no  more  come  in  contact 
with  the  liquid  through  which  it  is  passing  than  it  could  were  it 
inside  a  toy  balloon,  for  instance.  The  bubble  may  be  said  to  be 
enclosed  in  a  'liquid  skin.1'  Therefore  to  attach  this  bubble  to  any 
substance,  this  liquid  skin  must  first  be  penetrated  or  broken.  As 
seen  from  above,  this  requires  some  force. 

As  shown  above,  the  force  of  chemical  affinity  is  not  sufficient 
to  overcome  this  surface  tension.  So  then,  it  could  hardly  be  expected 
that  a  mere  adhesive  force  would  be  greater  than  this  surface  tension. 
Therefore,  to  attach  gas  to  solids  in  a  liquid,  it  is  first  necessary  to 
dissolve  the  gas  in  the  liquid  and  then  expel  it  in  a  nascent  state. 


iA  striking  experiment  to  show  these  liquid  films  is  as  follows:  To  a 
beaker  partly  filled  with  a  colorless  oil,  add  a  small  quantity  of  permanganate 
solution.  Blow  air  through  a  finely  drawn-out  glass  tube  into  the  perman- 
ganate solution  now  on  the  bottom  of  the  beaker.  Air  bubbles  enclosed  in 
the  colored  liquid  film  rise  through  the  oil  and  break  at  the  surface,  because 
of  the  expansive  force  of  the  gas.  The  colored  water  drops  back  through  the 
oil  exactly  in  the  same  manner  that  a  balloon,  bursting,  drops  to  the  earth. 


WHY  IS  FLOTATION?  139 

There  are  at  present  only  three  known  ways  of  forcing  a  gas 
mechanically  into  solution  so  that  it  actually  occupies  the  interstitial 
spaces  of  the  liquid  molecules:  (1)  beating  it  in  with  stirrers  or 
paddles,  as  is  described,  for  instance,  in  the  patent  papers  of  the 
Minerals  Separation  Co.,  where  propellers  or  centrifugal  pumps  are 
used;  (2)  dividing  it  into  such  minute  portions  that,  by  capillary 
force,  it  is  actually  taken  into  solution,  as  is  done  in  a  Callow  cell; 
and  (3)  introducing  it  as  a  surface  film  surrounding  a  jet  of  fluid 
by  means  of  surface  tension,  as  is  done  by  a  method  under  process 
of  patent. 

There  are  also  three  methods  of  expelling  dissolved  gas  from  a 
liquid  that  are  of  vital  interest  to  the  matter  in  hand;  (1)  Super- 
saturation,  so  that  the  excess  gas  comes  out  of  its  own  accord; 
(2)  heating,  which  expels  some  of  the  gas  by  increasing  its  volume; 
and  (3)  reduction  of  pressure.  The  present  Elmore  machines  work 
the  pulp  in  a  vacuum,  taking  advantage  of  the  fact  that  "at  constant 
temperature,  the  gas  dissolved  in  a  given  volume  of  liquid  varies 
directly  as  the  pressure" — Henry's  law. 

Since  it  is  easier  to  work  in  the  open  air  than  in  a  vacuum, 
flotation  machines  using  the  principle  mentioned,  of  forcing  more 
air  into  solution  than  the  liquid  can  hold,  are  preferable.  The 
second  method  mentioned,  of  expelling  dissolved  gas  by  heat,  aids 
the  super-saturation  type  of  machine  in  two  ways:  (1)  nascent  gas 
is  expelled  from  the  liquid  to  be  readily  attached  to  solids  for  flota- 
tion; and  (2)  dissolved  gas  is  expelled  from  the  solids  so  that  gas 
bubbles  may  be  easily  attached  to  them.  Here  lies  the  whole  secret 
of  flotation. 

No  solid  can  be  floated  unless  it  contains  some  dissolved  gas.  Why  ? 
For  the  reason,  explained  above,  that  the  enveloping  'liquid  skin' 
cannot  be  penetrated  or  broken.  It  was  shown  above  that  a  gas 
bubble  is  surrounded  by  a  film  of  liquid.  A  solid  in  a  liquid  is,  in 
the  same  way,  surrounded  by  a  film  of  the  liquid,  for  the  same  reason. 
Therefore,  in  a  liquid,  the  molecules  composing  the  film  around  a 
gas  bubble  would  have  no  more  attraction  for  those  composing  the 
film  surrounding  the  solid  than  they  would  have  for  any  molecules 
in  the  liquid  itself.  Hence  the  bubble  would  not  attach  itself  to 
the  solid.  It  is  seen  then  that  flotation  has  for  a  foundation  a  subject 
of  which  practically  nothing  is  known — occlusion  of  gases. 

It  is  self-evident  that  the  same  cause  which  tends  to  super- 
saturate a  liquid  with  gas  will  also  have  the  same  tendency  to 
super-saturate  a  solid  contained  therein.  And  also  the  same  cause 


140  THE   FLOTATION   PROCESS 

that  tends  to  dispel  from  solution  the  dissolved  gas  will  also  tend 
to  dispel  the  gas  from  a  solid  in  this  same  liquid.2  Therefore  a  solid 
in  a  liquid  becomes  a  nucleus  for  the  formation  of  bubbles.  This  is 
easily  demonstrated  by  the  formation  of  vapor  bubbles  when  water 
is  boiled. 

The  surcharging  of  a  liquid  with  a  gas  tends  to  surcharge  any 
solid  in  this  liquid — on  account  of  diffusion.  The  adhesion  of  the 
gas  for  the  solid,  therefore,  will  tend  to  condense  the  gas  on  the 
surface  of  the  solid.  Sufficient  condensation  will  collect  enough 
molecules  of  the  gas  to  form  a  bubble  on  the  surface  of  the  solid. 

The  same  effect,  due  to  diffusion  of  gas  in  the  opposite  direc- 
tion, will  be  produced  by  causing  the  gas  to  be  expelled  from 
either  the  liquid  or  a  solid  contained  in  this  liquid.  An  example 
of  this  is  the  dumping  of  a  cold  ore  into  the  hot  solution  of  a  flotation 
plant.  Bubbles  immediately  tend  to  form  on  the  ore  particles,  by 
reason  of  cohesive  and  adhesive  forces,  and  have  the  tendency  to  be 
enlarged  by  the  gas  in  solution  in  the  liquid. 

It  is  natural,  therefore,  to  suppose  that  solids  with  high  occlusive 
power  for  gases  have  a  greater  tendency  to  float.  Here,  then,  is  a 
cause  of  selective  flotation.  Hezekiah  Bradford's  patent  No.  345,951 
is  the  first  to  recognize  this.  Speaking  of  metallic  particles,  he 
states:  "These  floating  particles  appear  to  possess  some  peculiar 
qualities  which  repel  water  from  their  surfaces,  especially  when  such 
particles  are  exposed,  even  momentarily,  to  atmospheric  air3."  Later 
this  phenomenon  caused  trouble  to,  instead  of  benefiting,  Hebron, 
who  says  in  his  patent  No.  474,829,  an  interest  in  which  is  assigned 
to  Carrie  J.  Everson:  "I  expel  from  such  mineral  and  metal  par- 
ticles— the  air  and  other  gases — by  producing  as  far  as  practical  a 
vacuum — or,  and  preferably,  by  applying  heat  to  the  ore,  thereby 
obtaining  the  desired  expulsion  of  air  and  other  gases." 

Why  then  do  minerals  (here  in  these  patent  papers  meaning  solids 
containing  metal),  and  especially  sulphide  minerals,  occlude  gases 
more  readily  than  other  solids?  It  is  only  necessary  to  look  into  the 
subject  of  ore  deposition  for  the  answer.  Primary  sulphide  ores 
are  changed  near  the  surface  to  sulphates,  carbonates,  oxides,  etc. ; 


2"As  in  the  case  of  liquids,  we  would  expect  that  the  amount  of  gas 
adhering  to  the  surface  or  absorbed  in  the  pores  of  a  solid  would  vary  with 
the  nature  both  of  the  solid  and  of  the  gas,  with  the  extent  of  the  surface, 
with  the  fineness  of  the  pores  and  lastly  with  the  temperature,  becoming  less 
as  the  temperature  rose."  Josiah  P.  Cooke,  Jr.  'Chemical  Physics.' 

3He  describes  a  traveling  belt  with  one  end  in  water  to  take  advantage  of 
this  fact.  This  antedates,  and  is  the  same  principle  as,  the  Macquisten  tubes. 


WHY  IS  FLOTATION?  141 

in  other  words,  chemical  affinity  assists  sulphides  in  absorbing 
oxygen  or  carbon  dioxide.  Hebron  and  others  discovered,  by  the 
aid  of  the  microscope,  that  most  mineral  particles  to  be  saved  by 
concentration  have  larger  pores  and  surfaces  of  larger  extent  than 
equal  sized  'gangue'  particles.  This  gives  a  greater  chance  for 
gas  occlusion,  which  is  another  cause  of  selective  flotation. 

There  is  practically  no  adhesive  force  existing  between  oil  or 
fatty  substances  and  water.  As  a  general  rule,  an  oil  is  but  slightly 
soluble  in  water  or  water  in  oil.  Therefore  water  will  not  adhere 
to  a  surface  wetted  with  oil  or  oil  will  not  adhere  to  a  surface  wetted 
with  water.  Also  an  oil,  due  to  its  property  of  capillary  attraction, 
has  that  power  of  entering  solids.  Therefore,  owing  to  larger  surfaces 
and  pores,  most  metals  and  sulphides  are  capable  of  absorbing  oil 
so  that  sufficient  oil  can  be  attached  for  agglomeration  and  flotation. 
This  selective  flotation,  as  mentioned  above,  is  not  now  worth 
considering,  because  so  large  a  quantity  of  oil  is  necessary. 

Mickle's  experiments*  showed  that  none  of  the  minerals  tried 
hot,  cold,  or  with  reduced  pressure  floated  on  oil  under  any  of  the 
conditions  where  floating  would  take  place  on  water.  This  was  to 
be  expected,  since  the  specific  gravity  of  oil  is  less. 

What  then  is  the  potent  factor  for  selective  flotation  ?  It  is  the 
ability  to  vary  the  "angle  of  hysteresis5."  It  has  been  seen  from 
the  above  that  solids  occlude  gas  which  can  be  expelled  from  them. 
If  this  gas  be  expelled  from  them  when  they  are  in  a  liquid  at  a 
time  when  gas  is  expelled  from  the  liquid,  they  become  the  nuclei 
for  the  formation  of  gas  bubbles  which  will  float  them  under  certain 
conditions.  Now,  therefore,  if  it  be  possible  in  an  ore  mixture  to 
drive  out  a  considerable  portion  of  the  gas  from  all  the  particles, 
there  will  be  insufficient  remaining  in  the  'gangue'  to  float  it  while 
the  mineral  containing  more  gas  will  float  to  the  surface.  It  has 
been  found,  for  instance,  that  sulphuric  acid  in  very  small  quantity 
added  to  water  will  decrease  the  angle  of  hysteresis  to  that  point 
where  quartz  and  similar  '  gangue '  will  sink,  while  that  of  the  metallic 
particles  remains  practically  unchanged. 

Since  an  acid  in  very  minute  quantity  will  produce  this  effect,  it 
is  not  due  to  rise  in  temperature  or  reduction  in  pressure,  which 
would  drive  out  the  occluded  gas.  This  must  be  caused  then  by  no 
ordinary  phenomenon.  The  only  way  that  an  acid  can  act  in  this 
manner  is  in  the  capacity  of  an  electrolyte,  especially  when  diluted 


4Froceedings  of  the  Royal  Society  of  Victoria.    Vol.  23.    Part  2  of  1911. 
sTrans.  Inst.  M.  &  M.,  1912,  Presidential  Address  by  H.  L-.  Sulman. 


142  THE  FLOTATION  PROCESS 

to  its  dissociation  point.  That  is,  complete  ionization  exists.  Yet 
with  this  extreme  dilution,  gas  is  expelled  from  a  solid  contained 
therein.  In  other  words,  equilibrium  does  not  exist.  Why?  It  is 
on  account  of  these  ions  of  the  electrolyte  which  cause  this  displace- 
ment of  equilibrium  between  the  solution  and  the  gas  dissolved  in 
the  solids  within  this  solution.  This  then  resolves  itself  into  a  simple 
case  of  osmotic  pressure.  The  surface  of  the  solid  is  the  septum. 
The  ions  of  the  electrolyte  enter  the  solid  while  those  of  the  gas 
leave.  Since  the  carrying  solution  is  saturated  with  gas  already, 
bubbles  form;  and  this  action  continues  until  the  eutectic  point  is 
reached.  So  far  an  acid  (sulphuric  on  account  of  its  cheapness)  has 
been  used  as  the  electrolyte,  because  it  produces  such  a  great  change 
in  the  angle  of  hysteresis. 

In  the  future,  as  more  is  learned  concerning  flotation,  the  finer 
and  more  delicate  manipulation  will  be  better  understood,  permitting 
an  alkaline  electrolyte  to  be  commonly  used.  This  will  allow  of  the 
selective  action  for  mineral  particles  other  than  sulphides  so  that, 
for  instance,  cerussite  or  malachite  can  be  separated  readily  from 
gypsum,  quartz,  etc.  This  is  not  to  be  confused  with  Horwood's 
" differential"  or  ''preferential"  process,  whereby  the  surfaces  of 
some  sulphide  minerals  are  oxidized  by  roasting  to  prevent  them 
floating  with  another  sulphide  in  a  mixed  sulphide  ore. 

While,  as  stated  above,  the  fundamental  requisites  are  the  manu- 
facture of  'life-preservers'  and  the  attachment  of  these  to  the  min- 
eral particles,  it  is  still  necessary  to  rescue  these  particles.  Bubbles, 
on  coming  to  the  surface  of  a  liquid,  burst  if  not  protected,  and  the 
attached  mineral  particle  sinks.  Why  do  they  burst?  (1)  Relief  of 
pressure,  so  that  the  contained  gas  expanding  exerts  more  pressure 
on  the  liquid  film,  (2)  adhesive  force  of  contained  gas  for  the  atmos- 
phere, or  (3)  evaporation  of  the  film  causes  this  bursting.  The  greater 
the  super-saturation,  the  greater  the  interior  gas-pressure  of  the 
bubbles,  so  that  they  in  reality  explode.  This  is  the  case  with  bubbles 
in  a  glass  of  soda-water,  for  instance.  How  can  this  be  prevented? 
The  small  boy  will  prevent  it  by  coating  the  bubbles  with  soap — that 
is,  by  toughening  the  liquid  film.  This  then  is  the  secret  of  "the 
froth-forming  material"  so  frequently  mentioned  in  the  various  patent 
papers  of  the  Minerals  Separation  company.  Why  is  an  oil  the  most 
useful  substance  with  which  to  do  this? 

It  has  been  shown  above  that  metallic  particles  are  readily  coated 
with  oil.  Therefore,  an  oil  may  not  only  toughen  the  bubbles  but  a 
cohesive  force  is  exerted  on  the  oil-coated  metallic  particles.  Besides 


WHY    IS   FLOTATION?  143 

an  envelope  to  hold  the  gas,  an  aeronaut  uses  a  net  to  strengthen  his 
balloon,  so  that  when  the  pressure  is  relieved  by  the  higher  atmos- 
phere it  will  not  burst.  This  same  effect  is  obtained  in  froth-flotation. 
In  the  same  way  that  particles  form  around  drops  of  water  on  a  dusty 
floor  and  prevent  the  globule  from  breaking,  small  particles  form 
a  network  around  the  large  bubbles.  This  is  due  not  only  to  the  force 
of  cohesion  of  the  oil  on  one  particle  for  that  on  another,  but  the  force 
of  cohesion  existing  between  the  particles  themselves.  Thus  a  froth  is 
formed  of  bubbles  that  do  not  readily  break. 

It  is  a  well-known  fact  that  water  has  the  greatest  surface  tension 
of  all  liquids  under  ordinary  conditions,  except  mercury.  It  is  there- 
fore a  safe  assumption  that  dilution  with  another  liquid  will  decrease 
the  surface  tension.  The  tendency  to  float  is  decreased.  With  re- 
duced surface  tension  bubbles  burst  more  readily.  From  this  it  is 
easily  seen  that  surface  tension  is  decreased  exceedingly  by  the  use 
of  a  volatile  liquid.  Alcohol  evaporating  from  a  substance  held  near 
a  bubble  will  diffuse  sufficiently  to  readily  dilute  the  surface  film  and 
quickly  burst  it.  Mineral  particles  floated  when,  for  instance,  amyg- 
daloidal  or  globulous  eucalyptus  oil  is  used  will  dance  on  the  surface 
of  the  liquid,  being  apparently  attracted  and  repelled  until  evapora- 
tion has  progressed  sufficiently  to  equalize  the  surface  tension  not 
only  of  the  liquid  but  of  the  bubbles  as  well. 

"Water  then  is  the  natural  and  universal  medium  for  all  flotation 
machines  and  air  the  necessary  adjunct.  The  air  may  be  in  the  pores 
of  the  mineral  particles  and  as  films  around  them,  so  that  they  are 
not  easily  wetted,  in  which  case  the  machine  may  take  some  such 
form  as  a  Macquisten  tube  or  Henry  E.  Wood  type — a  purely  surface- 
tension  effect  into  which  enters  nothing  but  water  and  air.  The 
meniscus  of  the  water  buoys  up  the  metallic  particles  surrounded  with 
an  air  film  that  prevents  them  being  wetted.  The  force  of  gravity  is 
less  than  that  of  surface  tension,  so  the  particles  float.  If  the  particles 
be  surrounded  by  a  water-film,  the  cohesion  of  the  molecules  of  this 
film  for  those  of  the  body  of  water  neutralizes  the  surface  tension,  and 
gravity  sinks  the  particles.  Or  again,  minute  bubbles  may  be  attached 
to  metallic  particles  that  necessarily  contain  occluded  gas.  A  thin 
film  of  oil  may  enclose  or  contain  the  particles  and  their  attached 
bubbles.  With  sufficient  displacement  the  particles  will  rise  to  the 
surface  and  form  what  may  be  termed  a  DeBavay  float.  Or,  lastly, 
the  bubbles  may  be  large  and  have  the  mineral  particles  attached  to 
them,  as  well  as  being  attached  to  each  other.  This  is  the  so-called 
froth  flotation. 


144  THE  FLOTATION  PROCESS 

WHAT   IS   FLOTATION?— II 

By  T.  A.  RICKARD 
(From  the  Mining  and  Scientific  Press  of  October  2,  1915) 

All  of  the  natural  phenomena,  or  appearances,  described  at  the 
beginning  of  the  previous  article,  play  their  part  in  flotation  and 
each  of  them  has  served  as  the  basis  for  one  or  other  of  the  many 
patents  that  have  involved  the  subject  in  a  maze  of  vindictive 
litigation. 

SURFACE  TENSION  is  the  idea  underlying  Hezekiah  Bradford's  patent 
of  1886.  In  this  process  the  dry  powdered  ore  is  caused  to  meet  the 
surface  of  a  still  body  of  water,  so  that  the  metallic  particles,  which 
are  not  wetted,  are  made  to  float  away,  while  the  gangue  particles, 
which  are  wetted,  sink.  This  was  the  first  application  of  flotation 
without  the  aid  of  oil. 

In  1904  A.  P.  S.  Macquisten  invented  a  tube  apparatus  in  which 
surface  tension  is  utilized  for  concentration.  In  1906  the  process 
was  applied  on  a  working  scale  in  the  Adelaide  plant  at  Golconda, 
Nevada,  where  chalcopyrite  was  separated  from  a  lime-garnet  gangue. 
In  1911  the  Federal  Mining  &  Smelting  Co.  adopted  the  process  for  the 
Morning  mill,  at  Mullan,  Idaho,  in  the  separation  of  blende  and  galena 
from  a  quartz-siderite  gangue.  At  Golconda  96  tubes  treated  125 
tons  per  day;  at  Mullan,  119  tubes  treat  150  tons.  The  iron  tube  is 
6  ft.  long  by  12  in.  diameter.  The  interior  is  cast  with  a  helical  groove. 
The  tube  is  revolved  at  30  r.p.m.  Success  appears  to  depend  upon 
the  angle  at  which  the  metallic  particles  are  presented  to  the  surface 
of  the  water.  Subsequently,  the  water  at  Golconda  was  slightly 
acidified,  so  that  it  must  have  caused  an  ebullition  of  carbonic  acid 
gas  from  the  lime  in  the  ore.  Thus  the  bubble  phenomena  may  have 
come  into  play.  Later,  small  additions  of  coal-oil  were  made,  so  that 
another  phase  of  flotation  was  introduced.  In  the  first  instance,  how- 
ever, the  Macquisten  tube  was  a  real  surface-tension  process. 

In  1905  H.  L.  Sulman  and  H.  F.  K.  Picard  obtained  a  British 
patent  for  a  similar  process,  but  it  was  a  failure.  As  the  floating 
particles  are  in  the  nature  of  a  film,  or  "in  patches  one  particle  thick," 
the  area  of  the  separating  surface  has  to  be  large  and  still.  More- 
over, some  gangue-minerals  are  floated  as  readily  as  the  metallic  parts 
of  the  ore. 

In  1912  H.  E.  Wood  described  his  method  of  concentration,  by 
the  surface  tension  of  water  alone,  in  a  paper  read  before  the  American 


WHAT    IS   FLOTATION  ? II  145 

Institute  of  Mining  Engineers.  In  common  with  other  metallurgists, 
he  had  noticed  that  dry  particles  of  sulphide  minerals  are  ''good 
swimmers."  In  all  gravity  work,  we  try  to  drown  them.  He  had 
also  proved  for  himself  that  the  oxides  are  easily  wetted.  Thereupon 
he  devised  a  machine  in  which  the  dry-crushed  ore  is  fed  in  a  thin 
stream  from  a  vibrating  plate  onto  a  current  of  water.  An  impetus 
is  given  to  the  surface  by  small  water-jets.  By  retarding  the  current 
the  gangue  is  made  to  sink,  while  the  film  of  sulphides  remains  on 
the  surface.  The  elasticity  and  tenacity  of  this  film  is  remarkable. 
The  process  is  being  applied  on  a  commercial  scale  to  molybdenite 
ores  by  the  inventor,  Mr.  Wood,  at  Denver.  He  has  also  made  experi- 
mental demonstrations  on  graphite,  tellurides,  and  other  lustrous  min- 
erals. At  the  San  Francisco  del  Oro  mill,  in  Chihuahua,  Mexico,  12  of 
his  machines  are  in  use  on  an  ore  that  has  defied  other  efforts  at  con- 
centration. 

BULK-OIL  flotation  was  invented  by  Robinson  &  Crowder  in  1894 
and  developed  successfully  by  Francis  E.  Elmore,  whose  British 
patent  was  obtained  in  1898.  In  the  Elmore  process  the  crushed 
ore  is  mixed  with  several  times  its  weight  of  water.  With  this  pulp 
a  weight  of  oil  equal  to,  if  not  exceeding,  that  of  the  ore,  is  mixed 
gently,  so  as  not  to  break  or  emulsify  the  oil.  The  oiled  mass  is 
run  into  a  spitzkasten,  where  the  oil  rises  to  the  surface,  buoying 
the  metallic  particles,  while  the  gangue  and  water  are  removed  at  the 
bottom.  While  oil  is  described  as  the  prime  agent,  it  is  probable 
that  air,  entrained  by  agitation,  increased  the  buoyancy  of  the 
concentrate.1 

OIL  AND  Am.  Coming  to  processes  using  a  combination  of  oil  and 
air,  we  have  the  Everson  patent  of  1885.  Carrie  J.  Everson  was 
washing  some  sacks  in  which  concentrate  had  been  shipped  to  her 
brother's  assay-office  at  Denver  when  she  noticed  that  the  sulphide 
particles  floated  on  the  water.*  It  is  said  that  the  sacks  had  become 
greasy,  but  it  is  quite  likely  that  she  used  soap,  in  which  case  the 
greasiness  is  not  required  as  an  explanation.  In  her  process  the 
maximum  addition  of  oil,  namely,  18%,  is  less  than  one-sixteenth  of 
the  quantity  required  for  bulk  flotation.  As  to  air,  that  she  obtained 


iA  suggestion  that  is  confirmed  by  the  statement  of  Walter  McDermott 
that  "in  practice  [of  the  Elmore  process]  the  agitation  with  the  pulp  results 
in  the  oil  taking  up  a  very  appreciable  quantity  of  air,  giving  a  certain 
sponginess,  with  natural  increase  in  floating  power."  'The  Concentration 
of  Ores  by  Oil.'  E.  d  M.  J.,  February  14,  1903,  page  262. 

*This  proves  to  have  been  a  yarn.  See  page  35  of  this  book  and  'The 
Everson  Myth,'  Mining  and  Scientific  Press,  January  15,  1916. 


146 


THE   FLOTATION   PROCESS 


by  the  agitation  of  the  pulp  by  means  of  two  fans  radiating  from  a 
hollow  revolving  tube.  The  result — according  to  a  description  written 
in  1890,  not  in  the  light  of  prejudiced  observation  today — was  the 
formation  of  a  "thick  scum  of  sulphides"  that  "rose  to  the  surface 
and  was  skimmed  off,  leaving  the  hitherto  black  ore  as  white  as 
snow. '  ' 


FIG.    27.      THE    JANNEY    FLOTATION    MACHINE. 


The  original  bulk-oil  process  of  Elmore  had  numerous  applica- 
tions, some  of  which  were  fairly  successful,  but  in  1904  it  was 
displaced  by  the  Elmore  vacuum  process,  in  which  flotation  by  bulk- 
oil  was  subordinated  to  the  buoyant  effect  of  air-bubbles  generated 
from  the  oiled  mixture  while  under  a  vacuum,  and  by  heating.  Under 
normal  conditions  water  holds  in  solution  an  amount  of  air  equal  to 
2.2%  of  its  volume.  This  is  liberated  under  a  vacuum,  but  neither 
the  amount  of  air  released  (especially  at  high  altitudes)  nor  the 


WHAT    IS   FLOTATION? II  147 

quantity  of  oil  used  suffices  to  explain  the  degree  of  flotation  achieved, 
as  measured  in  weight  of  concentrate.  The  presence  or  the  addition 
of  limestone  or  other  carbonates,  with  the  use  of  acid,  suggests 
the  aid  of  bubbles  of  gas  other  than  air.  The  proportion  of  oil  in 
this  process  has  been  decreased  gradually  from  10  Ib.  per  ton  of  ore 
to  as  little  as  2.7  Ib.  per  ton.  As  the  mixing  involves  violent  agitation, 
it  seems  inevitable  that  entrained  air  plays  a  part. 

To  the  'oil  and  air'  process  we  must  add  that  of  Edmund  B. 
Kirby,  for  which  patent  was  applied  in  December  1903  and  granted 
in  January  1906.  Kirby  experimented  on  ore  from  Rossland,  British 
Columbia.  He  used  a  large  proportion  ("one-fourth  to  three-fourths 
as  much,  by  weight,  as  ore")  of  oil;  he  added  acid;  he  employed 
heat;  he  "thoroughly  agitated";  he  "injected  air  into  the  mass"; 
and  he  obtained  "a  floating  scum  of  hydrocarbon  liquid,  air,  bubbles, 
and  concentrates."  In  the  light  of  later  events  it  is  claimed  that 
he  must  have  made  a  'froth,'  because  the  oil  was  insufficient  to 
cause  bulk  flotation  and  the  agitation  sufficed  to  entrain  enough  air 
to  produce  a  froth.  To  this  the  patentees  of  the  so-called  'agitation- 
froth'  process  reply  that  his  "scum"  was  not  a  "froth"  in  their  sense 
of  the  term.  That  he  produced  froth  seems  highly  probable;  but  to 
say  that  'scum'  and  'froth'  are  the  same  thing,  is,  in  my  opinion, 
not  correct.2 

BUBBLES.  Meanwhile  the  bubble  methods  of  Charles  V.  Potter 
and  Guillaume  D.  Delprat  had  been  patented  in  1902.  In  these 
processes  gas  was  chemically  generated  with  a  view  to  promoting  the 
flotation  of  metallic  particles  in  Broken  Hill  ore.  This  Australian 
ore  contains  calcite,  which  by  the  addition  of  acid,  emits  bubbles 
of  gas  that  adhere  to  the  sulphides.  Potter  used  acid,  agitation, 
and  heat,  while  Delprat  employed  a  hot  solution  of  salt-cake  or  acid 
sodium  sulphate  and  sulphuric  acid.  Both  processes  were  successful 
on  a  large  scale,  particularly  Delp rat's,  which  is  still  in  use  at  the 
Broken  Hill  Proprietary  mine.  Neither  used  any  oil.  The  bubbles 
attach  themselves  to  the  sulphide  (blende  and  galena)  particles  and 
carry  them  to  the  surface,  whence  they  flow  with  the  liquor  into  a 
compartment  where,  the  bubbles  breaking,  the  metallic  freight  is 
dropped,  and  collected  as  a  mixed  concentrate.  T.  J.  Hoover  says3 
that  "the  result  of  the  manipulation  to  which  the  material  is  subjected 


2'Scum'  is  the  impurity  or  extraneous  matter  that  rises  to  the  surface  of  a 
liquid,  such  as  the  vegetal  film  on  a  stagnant  pond  or  the  dross  on  a  bath  of 
molten  lead.  'Froth'  is  a  multiplicity  of  bubbles. 

3'Concentrating  Ores  by  Flotation.'     Second  Edition.     Page  101. 


148  THE  FLOTATION  PROCESS 

is  the  formation  of  a  dense  froth  of  bubbles  and  mineral";  but  this 
was  published  in  1912,  and  must  be  read  in  the  light  of  events  long 
subsequent  to  the  claims  made  by  either  Potter  or  Delprat.  In  order 
to  explain  the  making  of  froth  without  oil,  he  suggests  the  presence 
in  the  ore  of  such  substances  as  "yield  gummy  organic  compounds 
that  selectively  adhere  to  the  ore."  This  is  an  important  suggestion. 
Be  that  as  it  may,  the  Potter  and  Delprat  methods  demonstrate  that 
flotation  is  practicable  by  the  aid  of  bubbles  without  the  addition 
of  oil. 

In  the  Froment  process,  patented  in  Great  Britain  and  Italy  in 
June  1902,  the  bubble  idea  is  dominant,  for,  while  Alcide  Froment 
used  oil,  he  employed  it  to  attract  the  bubbles  of  gas  generated  by 
the  reaction  between  acid  and  calcite,  adding  the  latter  if  suitable 
carbonates  were  lacking  in  the  ore.  He  emphasized  the  fact  that 
not  only  have  the  lustrous  metallic  particles  an  affinity  for  films  of 
oil,  but  the  oil  itself  attracts  bubbles  of  gas,  both  air  and  carbon 
dioxide.  He  recommends  much  less  oil  than  had  hitherto  been  used, 
namely,  a  "thin  layer  of  oil,"  which  has  been  interpreted,  according 
to  the  exigencies  of  litigation,  to  mean  anything  from  less  than  1% 
up  to  14%,  according  as  the  Froment  patent  was  being  upheld  or 
attacked.  In  Froment 's  later  instructions  to  the  purchasers  (Minerals 
Separation,  Ltd.)  of  his  patent  he  mentioned  the  quantity  as  from 
1  to  3J%.  For  a  5%  sulphide  ore,  the  oil  would  weigh  20  Ib.  per 
ton.  This  question  of  the  quantity  of  oil  required  by  Froment  has 
been  much  discussed,  but  the  dominant  idea  in  his  mind  appears  to 
have  been  the  affinity  of  oiled  particles,  necessarily  sulphides  or 
lustrous  metallic  particles,  for  bubbles  of  gas.  These  he  obtained 
by  agitation  (air-bubbles)  and  by  adding  both  acid  and  calcite 
(bubbles  of  carbonic  acid  gas)  to  the  pulp.  As  to  what  "a  thin  layer 
of  oil"  may  mean,  I  do  not  know  what  Froment  intended  by  the 
expression,  but  the  scientific  meaning  of  the  phrase  is  indicated  by 
the  fact  that  oil  when  dropped  on  the  surface  of  water  will  spread 
out  in  a  film  one  molecule  thick.4 

The  agitation  of  the  ingredients  specified  by  Froment  will  pro- 
duce a  froth;  therefore,  to  the  detached  onlooker,  it  is  difficult  to 
distinguish  the  essentials  of  his  process  from  those  claimed  in  the 
basic  patent  of  Minerals  Separation.  Mr.  Sulman  called  the  Froment 
froth  a  "tender  and  evanescent  assemblage  of  bubbles  of  carbon 


4<0il  Films  on  Water  and  on  Mercury.'  By  Henri  Devaux.  Translated  and 
published  in  Annual  Report  of  Smithsonian  Institution,  1913.  Also  M.  d-  S.  P., 
July  31,  1915,  page  156. 


WHAT    IS    FLOTATION? II  149 

dioxide  carrying  mineral,"  but  if  it  carried  mineral  I  do  not  see  that 
his  refusal  to  call  it  'froth'  is  of  any  great  consequence  to  those  of 
us  who  are  not  interested  in  the  litigation. 

COAGULATION.  Here  we  come  to  what  is  apparently  a  break  in 
the  sequence  of  inventiveness,  for,  beginning  with  November  1902, 
Arthur  E.  Cattermole  obtained  a  succession  of  patents  for  a  process 
in  which  the  idea  of  oil-selection  is  used  to  sink  the  metallic  particles 
of  an  ore,  not  to  float  them.  To  an  acidified  pulp  he  added  from 
4  to  6%  "of  the  weight  of  metalliferous  matter  present,"  not  of  the 
ore  as  a  whole;  therefore,  with  a  12%  zinc  ore  this  would  mean  0.48 
to  0.72%,  say  10  to  15  Ib.  oil  per  ton  of  ore;  and  with  a  2%  copper 
ore,  it  would  mean  only  IJ-to  2J  Ib.  -of  oil.  But  this  oil  "is  brought 
into  the  condition  of  an  emulsion  in  water  containing  a  small  per- 
centage of  soap  or  other  emulsifying  agent."  These  are  the  words 
of  his  most  important  patent,  U.  S.  No.  777,273,  dated  December  13, 
1904,  but  in  his  first  patent,  British  No.  26,295,  of  November  28, 
1902,  he  gives  the  proportion  of  soap  as  2%.  When  this  mixture  of 
ore,  acidulated  water,  and  soapy  oil  is  agitated  violently  the  metallic 
particles  are  agglomerated  into  flocculent  masses  that  sink,  the  sep- 
aration from  the  gangue  being  then  effected  by  an  up-current  of  water. 
To  facilitate  the  separation,  the  mixing  was  conducted  in  two  stages, 
of  which  the  second  is  said  to  have  been  "a  rolling  form  of  agitation." 
Cattermole  called  his  agglomerate  a  '  granule ' ;  Froment  called  it  a 
'  spherule. ' 

FROTH.  The  Minerals  Separation  company  was  organized  in  1903 
to  acquire  the  Cattermole  invention  and  thereafter  his  patents  became 
part  of  the  property  of  that  company.  The  first  and  only  plant  to 
use  the  Cattermole  process  was  erected  on  the  Central  mine  at  Broken 
Hill,5  where  it  was  soon  displaced  by  the  so-called  agitation-froth 
process  of  Sulman,  Picard,  and  Ballot.  These  gentlemen  have  testi- 
fied that  they  made  their  discovery  by  experimenting  with  the  Cat- 
termole process,  applying  scientific  methods  of  research,  based  on  the 
fact  that  sometimes  "loose  flocculent  masses  of  partially  granulated 
sulphides"  would  rise,  instead  of  sinking.  Finally,  they  decided  that 
this  was  due  to  insufficient  oil.  The  actual  experiments  were  made 
by  Arthur  H.  Higgins,  who,  by  diminishing  the  ^amount  of  oil  to 
0.62%  on  the  ore,  caused  so  many  of  the  metallic  particles  to  rise  that 
a  high  recovery  was  obtained  by  flotation.  H.  L.  Sulman  says  that 
by  reducing  the  amount  of  oil  the  granulation  was  stopped  and  "co- 


s'Flotation  at  Broken  Hill.'     By  James  Hebbard.     Mining  and  Scientific 
Press,  September  4,  1915.    See  page  110  of  this  book. 


150 


THE   FLOTATION   PROCESS 


incidentally  a  mineral  froth  began  to  take  its  place."  This  was  in 
March  1905.  Whereupon  the  British  patent  of  Minerals  Separation  No. 
7803,  of  April  12,  1905,  was  taken  out  by  H.  L.  Sulman,  H.  F.  K. 
Picard,  and  John  Ballot,  and  subsequently  they  obtained  the  U.  S. 
patent  No.  835,120  of  May  29,  1905,  issued  on  November  6,  1906.  In 
this  patent  reference  is  made  to  the  Cattermole  patent  and  it  is 


J.  M.  HYDE. 
ART  OF  CONCENTRATION  OF  MINERAL  SUBSTANCES. 

APPLICATIOH  FIL£D  HOT.  10,  1911. 


1,022,085. 


Patented  Apr.  2, 1912. 


FlO.  28.      FACSIMILE  OF  HYDE'S  PATENT,   AS  USED  AT  THE  BUTTE  &  SUPERIOR  MINE. 


WHAT    IS    FLOTATION? II  151 

claimed  that  the  'granulation'  characterizing  his  method  is  stopped 
by  reducing  the  amount  of  oil  to  "a  fraction  of  1%  on  the  ore"  and 
that  by  vigorous  agitation  the  oil-coated  particles  are  caused  "to  rise 
to  the  surface  of  the  pulp  in  the  form  of  a  froth  or  scum."  The  use 
of  'scum*  here  is  unfortunate  for  Minerals  Separation,  for  it  tends  to 
identify  the  'froth'  made  by  this  process  with  the  'scum'  made  by 
most  of  their  predecessors  in  the  art.  In  this  patent  acidulated 
water,  warming  of  the  mixture,  oleic  acid  from  0.025  to  0.5%  on 
the  ore,  oleic-soap  solution,  the  formation  of  the  froth,  and  the  sep- 
arating of  the  froth  from  the  remainder  of  the  solution  are  specified. 
Since  this  patent  was  issued  the  process  has  been  applied  successfully, 
and  on  a  large  scale,  in  many  parts  of  the  world,  notably  Broken 
Hill,  Great  Cobar,  Great  Fitzroy,  Chillagoe,  and  Wallaroo,  all  in 
Australia ;  also  the  Braden  copper  mine  in  Chile ;  and  more  recently 
at  -the  Inspiration,  Anaconda,  and  other  important  mines  in  this 
country.  It  is  proper  to  add  that  a  froth-flotation  process  is  used 
successfully  at  the  Butte  &  Superior,  Miami,  and  other  mines,  but 
the  users  deny  that  it  is  a  method  to  which  the  Minerals  Separation 
company  has  proprietary  rights.  The  difference  of  opinion  is  yet 
to  be  settled  by  the  Courts. 

In  the  foregoing  review,  I  have  omitted  reference  to  a  number 
of  flotation  patents,  some  of  them  interesting,  because  the  multiplica- 
tion and  repetition  of  detail  would  be  only  confusing.  It  will  be 
noted  that  the  amount  of  oil  per  ton  of  ore  has  decreased  from  over 
a  ton6  to  less  than  half  a  pound.  From  an  insistence  upon  the  use  of 
acid  in  all  the  patents,  even  to  the  last  quoted  in  the  above  summary, 
we  come  to  the  recent  fact  of  flotation  in  alkaline  solutions.  Indeed, 
in  the  case  of  the  Mexican  mill  we  are  told  that  the  deleterious  effects 
of  soluble  sulphates  was  overcome  by  an  excess  of  oil.7  How  much 
of  the  oil  used  in  the  prior  art  was  due  to  excess  of  acid,  it  remains 
to  be  stated  by  an  independent  investigator.  Much  of  the  early 
work  with  flotation  was  done  on  Broken  Hill  ore,  which  contains  a 
notable  proportion  of  carbonates,  hence  the  addition  of  acid  proved 
a  help,  by  generating  gas,  not  only  in  the  Potter  and  Delprat 
processes,  but  in  others  also,  namely,  those  using  oil.  One  ingredient, 
however,  has  gained  progressively  in  importance:  air.  Other  gases 
have  had  their  day,  some  generated  chemically,  others  electrolytically, 


e'Notes  on  the  Elmore  Concentration  Process.'  By  Charles  M.  Rolker. 
Trans.  Inst.  M.  &  M.,  London.  Vol.  VIII,  1899-1900,  page  382. 

T Mining  and  Scientific  Press,  July  24,  1915,  page  124.  See  page  94  of 
this  book. 


152 


THE   FLOTATION    PROCESS 


but  in  the  latest  phase  of  the  process  the  prime  agent  is  air.  Indeed, 
the  good  results  ensuing  from  the  lessened  proportion  of  oil  may 
be  due  to  the  fact  that  the  less  the  oil  the  greater  the  intensity  of 
agitation  required  to  spread  it  throughout  the  pulp.8  The  vigorous 

H.  L.  SULMAN,  H.  H.  GREENWAY  &  A.  H.  HIGGINS. 

ORE  CONCENTRATION. 

APPLICATION  FILED  APR.'  30",  1909. 

962  678.  Patented  June  28, 1910. 


FIG.  29.   ONE  OF  THE  MINERALS  SEPARATION  PATENTS. 


^Dudley  H.  Norris  has  several  patents  for  the  use  of  water  containing,  in 
solution,  air  under  high  pressure  for  intensified  bubbling,  with  or  without  oil. 


WHAT    IS   FLOTATION? II  153 

agitation,  so  often  emphasized,  may  have  been  like  the  shot  that 
was  aimed  at  the  crow  and  killed  the  pigeon,  for  it  must  have  done 
more  than  mix  the  ingredients :  it  resulted  in  entraining  and  atomizing 
a  large  volume  of  air.  The  later  history  of  flotation  suggests  that 
a  day  may  come  when  the  oil,  like  the  acid,  will  be  found  non- 
essential,  and  in  its  place  will  be  added  the  ingredient  that  supplies 
the  substance  required  for  making  bubbles.  To  make  bubbles  the 
surface  tension  of  the  water  in  the  flotation-cell  must  be  decreased 
by  a  contaminant  and  at  the  same  time  the  viscosity  of  the  liquid 
must  be  strengthened.  Oil  is  not  the  only  substance  that  can  perform 
these  functions.  Some  alkaline  compound  may  be  found  that  will 
do  the  trick.  In  the  Cattermole,  Sulman  &  Picard  patent  (U.  S. 
777,274)  a  fatty  acid  is  produced  in  situ.  In  another  patent,  by 
Sulman.  Greenway  &  Higgins  (U.  S.  962,678)  a  claim  is  made  for 
"an  organic  compound  contained  in  solution  in  the  acidified  water" 
as  a  soluble  frothing  agent.  In  U.  S.  1,055,495,  Schick  claims  the 
use  of  carbon  tetra-chloride  to  promote  '  levigation, '  or  flotation.  In 
U.  S.  770,659,  Scammell  employs  sulphur  dioxide  as  a  means  for 
increasing  the  viscosity,  and  in  U.  S.  744,322,  Foote  uses  slaked  lime. 
Among  other  nostrums,  alcohol,  phenol,  camphor,  amyl  acetate, 
benzoic  and  lactic  acids,  and  calcium  chloride  have  been  suggested 
in  various  patents.  In  some  cases,  possibly,  an  ingredient  of  the 
ore  itself  may  suffice.  Meanwhile  the  element  of  time  essential  to  a 
good  formation  of  froth  suggests  that  the  delay  is  useful  in  increasing 
the  viscosity.  Mere  speed  of  agitation  and  aeration  does  not  seem 
to  suffice.  But  sub-division  of  the  air  helps.  This  reminds  us  that 
T.  J.  Hoover  and  Minerals  Separation  took  out  a  patent,  in  Great 
Britain  in  1910,  for  the  introduction  into  the  oiled  pulp  of  air  and 
other  gases  through  a  permeable  medium,  but  it  was  not  deemed 
worth  while  to  obtain  a  patent  in  the  United  States.  Knowing  nothing 
about  this,  J.  M.  Callow  hit  upon  the  same  idea  and  designed  the 
porous  bottom  now  in  use  at  many  flotation  plants.  Cattermole 
used  an  ordinary  cone  or  Gabbett  mixer9  fitted  with  baffles.  Froment 
employed  a  mixer  of  the  egg-beater  type.  Sulman  &  Picard  in  one 
of  their  patents  (U.  S.  793,808)  suggest  an  agitator  made  of  a  coil 
of  perforated  gas-pipe,  through  which  compressed  air  and  oil  are 
fed.  Centrifugal  pumps,  Pachuca  agitators,  air-jets,  and  pans  with 
mechanical  stirrers  have  been  adopted  by  various  inventors.  Other 
devices  for  causing  agitation  and  promoting  aeration  of  the  pulp 
have  been,  and  are  being,  introduced. 


»See  Pig.  41. 


154  THE  FLOTATION  PROCESS 

SURFACE  TENSION  AND  SALTS  IN  SOLUTION 

(From  the  Mining  and  Scientific  Press  of  October  9,  1915) 

The  Editor: 

Sir — In  your  editorial  on  'Flotation  at  Broken  Hill'  in  your  issue 
of  September  4,  1915,  page  343,  you  made  a  statement  regarding 
surface  tension  that  is  rather  befogging  to  a  student  of  flotation. 
It  is  as  follows:  ''Mr.  Hebbard  says  that  the  surface  tension  was 
increased  by  the  salts  introduced,  but  we  venture  to  suggest  that 
the  opposite  was  the  fact." 

Surface  tension  has  been  threshed  out  pretty  thoroughly  by 
articles  appearing  in  the  Journals  of  the  American  Chemical  Society, 
beginning  in  1908. 

Jour.  Am.  Chem.  Soc.,  Vol.  XXX,  No.  3,  March  1908 

"  7,  July  1908 

"  XXXIII,  "  3,  March  1911 

"  5,  May  1911 

"  7,  July  1911 

"  XXXV,  "  10,  October  1913 

"  11,  November  1913 

"  12,  December  1913 

These  articles  deal  with  the  drop-weight  method  (weight  of  a 
falling  drop)  for  the  determination  of  molecular  weight,  critical 
temperature,  and  surface  tension,  and  they  describe  the  apparatus 
used.  The  work  was  started  by  Morgan  and  Stevens,  who  wished 
to  investigate  what  had  become  known  as  the  law  of  Tate. 

Tate,  in  1864,  had  made  a  generalized  statement  about  the  relation 
of  weight  of  drop  to  diameter  of  tube,  the  weight  that  could  be  raised 
by  capillary  action,  and  the  temperature  of  the  drop.  Some  of  their 
conclusions  are  that: 

(a)  The  drop-weight  of  any  liquid  is  proportional  to  the  diameter 
of  the  dropping- tube.  These  tubes  are  unifrom  in  diameter,  thus 
differing  from  the  ordinary  burettes. 

(6)  The  weight  of  a  drop,  other  things  being  the  same,  is  propor- 
tional to  the  surface  tension  of  the  liquid.  * 

(c)  That  it  is  possible  to  calculate  the  temperature  at  which  the 
drop-weight  would  become  zero,  namely,  the  critical  temperature  of 
the  liquid,  for  at  that  point  the  drop  would  disappear,  there  being 
no  distinction  between  the  gas  and  the  liquid. 

In  the  course  of  these  experiments  the  surface  tension  of  a  number 


SURFACE  TENSION  AND  SALTS  IN  SOLUTION 


155 


of  organic  liquids  in  aqueous  solution  was  determined  by  drop-weight 
and  found  to  range  from  21  up  to  that  of  water.  The  tabulated 
results  cover  several  pages  in  the  Journal;  I  have  copied  a  part  and 
condensed  into  one  table,  which  is  given  below. 


Ethyl 


0.000 

0.979 

2.143 

4.994 

10.385 

17.979 

25.000 

50.000 

75.000 

100.000 


AQUEOUS  SOLUTIONS  AT  30  °C. 

alcohol.—^  ,— Amyl 

Sur.  ten.  % 

71.030  0.000 

68.120  0.250 

64.845  0.500 

60.294  0.750 

53.661  1.000 

48.817  1.500 

41.809  2.000 

31.843  2.498 

26.173  

21.037  100.000 


alcohol.-^ 

r-Met 

Sur.  ten. 

% 

71.030 

0.000 

65.600 

1.011 

60.847 

2.500 

53.137 

4.097 

44.668 

9.994 

37.311 

10.000 

32.941 

25.000 

26,521 

50.000 

23.850 

75.000 

20.756 

100.000 

,  —  Acetic 

acid.—  ^ 

%     Sur.  ten. 

0.000 

71.030 

1.000 

67.756 

2.475 

63.995 

5.001 

59.435 

10.010 

53.500 

14.980 

49.451 

20.090 

46.455 

49.960 

37.109 

79.880 

31.026 

100.000 

25.725 

alcohol.—^ 
Sur.  ten. 
71.030 
53.712 
46.157 
41.247 
37.631 
32.504 
28.667 
25.726 


22.296 


0.000 

1.000 

2.500 

5.000 

10.000 

15.000 

25.000 

50.000 

75.000 

100.000 


Formic  acid.— > 
>  Sur.  ten. 
71.030 
69.816 
68.024 
65.706 
62.061 
59.197 
55.190 
48.112 
41.990 
35.281 


It  is  to  be  noted  that  in  all  cases  the  very  first  addition  causes  a 
very  considerable  lowering  of  surface  tension.  The  decrease  in 
the  surface  tension  of  water  caused  by  the  addition  of  a  very  small 
.amount  of  amyl  alcohol  is  especially  striking.  Thus  the  presence  in 
solution  of  even  so  small  an  amount  as  0.25%  changes  the  surface 
tension  of  water  from  71.03  to  53.7,  or  nearly  25%  at  30°  C. 

Morgan  and  Schramm  studied  many  concentrations  of  a  few  salts. 
They  selected  the  molten  hydrated  salts  for  this  purpose;  those 
salts  which  melt  below  50°  in  their  own  water  of  crystallization 
being  especially  satisfactory  for  this  purpose,  for  the  reason  that 
concentration  in  some  of  these  cases  could  even  be  carried  to  super- 
saturation. 

In  the  case  of  the  salts  which  they  studied  it  is  plain  that  surface 
tension  is  increased  by  the  salts  introduced.  Where  calcium  chloride 


156 


THE   FLOTATION   PROCESS 


was  used,  the  surface  tension  was  increased  from  71.03  to  102.57, 
approximately  50%.  Taking  a  few  specific  cases  it  is  noted  that  to 
increase  the  surface  tension  10%  it  would  take 

20%  CaCl2  at  30° 
43%  Zn  (N08)  at  45° 
29%  Na^CK^  at  30° 
34%  NaAOs-at  40° 


The  diagram  is  appended.     See  Fig.  30. 


*o 
| 

rs 


o  s  so  /s  ^o  ^5  so  35  to  45  so  55 

(y/77,  sa//oe/~/OOdm*  so/uTJon 
FIG.  30. 

The  degree  of  accuracy  of  Valson's  early  generalization  that 
equivalent  salt  solutions  exhibit  identical  values  of  surface  tension 
is  shown  by  plotting  the  same  results  reduced  to  molecules  of  water 
to  molecules  of  salt.  But  one  must  be  careful  not  to  carry  generaliza- 
tions too  far  because  this  does  not  hold  with  some  salts.  The  diagram 
is  appended.  See  Fig.  31. 

The  fact  is  that  some  salts  elevate  while  other  depress  surface 
tension,  but  the  former  predominate.  In  addition  to  the  salts  just 
mentioned,  the  tartrates,  carbonates,  oxalates,  citrates,  lactates,  and 
a  part  of  the  acetates  raise  surface  tension ;  while  the  salicilates,  the 
butyrates,  part  of  the  acetates,  and  all  the  acids  lower  surface  tension. 

It  is  suggested  that  the  liberation  of  free  acid  by  hydrolysis  in 
the  case  of  salts  of  weak  acids  may  cause  their  negative  effect  on 
water. 


SURFACE    TENSION    AND    SALTS   IN    SOLUTION 


157 


All  acids  lower  surface  tension,  and  in  the  case  of  the  fatty  acids 
experiments  have  shown  that  the  lowering  is  proportional  to  the 
carbon  content  of  the  acid. 

It  is  suggested  in  these  researches  that  the  surface  tension  of  a 


k 


S   /O    S3  2O  Z£  30  35 
/7o/e*    wafer  oer  rr?o/e. 

FIG.  31. 


5b 


solution  of  two  salts  one  of  which  raises  the  surface  tension  and  the 
other  lowers  it,  is  an  additive  property  of  the  two  solutions — provided 
no  chemical  reaction  takes  place  between  them,  and  the  values  of 
the  two  are  not  far  removed  from  the  value  of  water.  If  one  of  the 
solutes  causes  a  much  larger  effect  than  the  other,  the  value  of 
the  mixture  lies  closer  to  the  one  with  the  greater  effect. 

Regarding  the  variation  of  surface  tension  with  temperature, 
it  is  made  clear  that  surface  tension  increases  with  decrease  in 
temperature. 

In  reviewing  the  subject  of  flotation  in  one  of  the  mining  journals 
about  two  years  ago,  a  leading  educator  made  the  statement  that 
heat  increases  surface  tension.  Now  this  is  absolutely  erroneous  in 
case  of  pure  water  and  it  is  not  likely  that  it  would  maintain  in 
any  case.  I  do  not  mention  this  in  a  fault-finding  spirit,  but  to 
show  that  in  the  science  of  flotation  the  metallurgical  engineer  faces 
problems  in  physics  and  chemistry  that  are  absolutely  new  to  him. 

In  the  work  in  the  chemical  journals  the  surface  tension  of  pure 
water  is  taken  as  71.03  dynes  per  cm.  at  30°,  69.33  at  40°,  and  68.46 


158  THE  FLOTATION  PROCESS 

at  45°,  while  Hooverf  uses  81  with,  apologies.  Again  Hoover  makes 
a  slip  on  page  77  where  he  says  that  surface  tension  of  water  has 
been  determined  to  be  a  force  of  81  dynes  per  square  centimetre. 
Here  he  has  confused  surface  tension  in  dynes  per  centimetre  with 
surface  energy  in  "ergs  per  sq.  cm."  Work  (in  ergs)  is  the  act  of 
producing  a  change  in  opposition  to  a  force  (in  dynes)  that  resists 
this  change.  Now,  gravity  gives  to  a  gram  a  velocity  of  980  cm.  per 
second.  It  is  therefore  equal  to  980  dynes.  Hence  if  one  gram  be 
lifted  vertically  one  centimetre,  the  work  done  against  gravity  is 
980  ergs.  Books  on  physics  demonstrate  that  surface  tension  (dynes) 
per  unit- width  is  numerically  equal  to  surface  energy  (ergs)  per 
unit-area.  We  should  therefore  speak  of  surface  tension  in  dynes 
per  centimetre,  and  surface  energy  in  ergs  per  square  centimetre. 

The  above  figures  on  surface  tension  and  surface  energy  might 
be  applied  to  the  so-called  surface  tension  method  of  notation,  such 
as  the  Wood  machine,  where  the  ore  is  fed  dry  onto  the  surface  of 
water  and  at  one  place  at  least,  in  the  West,  where  the  wet  oiled  pulp 
is  spread  upon  the  surface  of  water  in  a  spitzkasten. 

While  0.0724  gm.  (71.03-^-981)  per  sq.  cm.  represents  the  weight 
that  it  requires  to  just  break  the  surface  membrane  of  pure  water, 
there  is  another  factor,  and  that  is  the  size  of  the  dimple  formed. 
Take  the  case  of  galena.  The  buoyant  factors  are  the  membrane 
and  the  water  displaced.  Taking  the  specific  gravity  of  galena  at 
7.5,  the  maximum  volume  of  a  dimple  on  one  square  centimetre 
would  be  0.0096  cc.  (0.0724-^-7.5)  or  a  displacement  equal  to 
0.0096  gm.  water.  Adding  the  two  quotients  we  find  that  0.082 
(0.0724  +  0.0096)  gm.  galena  per  sq.  cm.  would  just  break  through. 
This  is  not  mathematically  correct,  but  a  close  approximation — 
sufficiently  close,$  because  we  do  not  know  the  volume  of  the  foreign 
water  attached  and  the  condition  of  the  water. 

WILL  H.  COGHILL. 
El  Paso,  Texas,  September  24. 


t'Concentration  of  Ores  by  Flotation,'  2nd  edition. 
JSee  page  348  of  this  book. 


AIR-FROTH    FLOTATION  159 


AIR-FROTH   FLOTATION 

(From  the  Mining  and  Scientific  Press  of  October  16,  1915) 
A  LEGAL  VERSION  OF  THE  TECHNOLOGY  OF  THE  PROCESS 

[Herewith  we  give  a  part  of  the  address  made  by  Mr.  Walter  A. 
Scott,  counsel  for  defendants  in  the  case  of  Minerals  Separation  v. 
Miami  recently  tried  at  Wilmington,  Delaware.  We  give  this  not 
only  because  the  learned  gentleman  discusses  the  underlying 
principles  of  the  flotation  process  in  an  interesting  way  but  because 
the  questions  put  by  the  Judge  are  such  as  would  suggest  themselves 
to  other  persons  curious  to  understand  the  subject.  In  reading  this 
excerpt  from  the  court  proceedings  our  readers  must  not  forget  that 
it  is  an  ex  parte  statement,  putting  forth  the  technology  of  the  subject 
with  a  view  to  aiding  the  case  for  the  defendant.  Mr.  Scott  assumes 
that  oil  is  necessary  to  flotation  and  also  that  the  force  of  surface 
tension  bursts  the  bubbles.  Neither  of  these  assumptions  can  be 
taken  for  granted  in  a  scientific  discussion,  however  useful  they  may 
be  in  a  lawyer's  brief. — EDITOR.] 

The  manifestation  of  the  force  of  surface  tension  is  a  phenomenon 
that  shows  itself  as  a  tendency  of  any  liquid  body — we  may  confine 
ourselves  to  a  liquid — to  assume  that  shape  in  which  it  has  the  least 
surface.  It  is  a  well-known  fact  that  in  the  form  of  a  sphere  the 
ratio  of  surface  to  volume  is  at  the  minimum.  Therefore  we  can 
say  that  surface  tension  is  that  force  or  property  which  tends  to 
cause  a  body  of  liquid  to  assume  the  spherical  form,  in  order  to 
make  its  surrounding  surface  as  small  as  possible. 

We  are  familiar  with  manifestations  of  this  force;  when  a  drop 
of  water  falls  upon  a  hot  stove,  we  see  it  immediately  come  into  the 
form  of  a  little  sphere.  The  explanation  of  that  probably  is  that 
the  stove,  being  hot,  generates  a  little  steam  all  around  the  particles, 
and  that  frees  it  from  interference  by  other  forces,  so  that  it  assumes 
the  shape  which  surface  tension  tends  to  give  it. 

I  think  the  ordinary  shot-tower,  where  molten  lead  when  poured 
or  dropped  assumes  the  spherical  form  of  shot  is  probably  another 
manifestation  of  surface  tension.  The  lead,  instead  of  dropping  in 
a  formless  mass  as  it  passes  through  the  air,  under  the  influence 
of  the  contractile  force  around  its  surface  is  drawn  up  into  a 
spherical  body. 

Another  illustration  is  the  tendency  which  we  observe  when  water 


160  THE  FLOTATION  PROCESS 

is  spilled,  we  will  say,  upon  a  smooth  surface  or  table.  Were  it  not 
for  surface  tension  it  would  spread  out  in  an  infinitely  thin  layer; 
gravity  would  tend  to  pull  it  down  flat.  But  surface  tension  causes 
it  to  assume  the  form  of  a  little  bulge  of  water  on  the  table.  Viscosity 
of  the  water  probably  also  plays  a  part  in  that.  It  is  difficult  to 
disentangle  all  of  these  causes.  But  surface  tension  surely  is  one 
of  the  forces  to  enter  into  that  effect. 

Now,  this  surface  tension  exists  not  only  at  the  free  air-surface 
(for  instance,  the  surface  of  the  water  in  this  glass)  but  it  exists 
at  every  point  where  there  is  a  change  of  medium,  that  is,  where 
the  water  encounters  another  substance.  Surface  tension  here  is 
along  the  water  surface,  the  air  surface,  but  that  surface  tension 
exists  clear  around  the  inner  surface  of  the  glass  and  at  the  bottom 
of  the  glass;  it  has  the  same  relation  to  the  water  around  the  glass 
and  at  the  bottom  of  the  glass  as  next  the  atmosphere  above.  So 
this  surface  tension  exerts  itself  about  the  entire  surface  of  a  body 
of  liquid,  tending  to  draw  it  into  a  spherical  form. 

As  we  observe  a  bubble — for  instance,  a  soap-bubble — the  idea 
that  we  are  apt  to  have  is  that  the  bubble  bursts  from  an  interior 
force ;  that  is,  that  it  explodes.  We  are  accustomed  to  that  thought 
in  connection  with  any  explosion  or  bursting.  I  apprehend  from 
the  testimony  of  these  experts  that  a  lessening  of  this  contractile 
force,  or  the  surface  tension,  tends  to  permanency  of  a  froth;  from 
that  fact  I  apprehend  that  the  force  causing  a  bubble  to  burst  is 
not  an  expansive  force  from  the  inside,  but  that  it  is  due  to  surface 
tension,  if  the  surface  tension  is  strong  enough.  For  instance,  imagine 
a  soap-bubble,  we  will  say,  three  inches  in  diameter.  It  is  surrounded 
by  a  very  thin  film  of  water  contaminated  or  modified  by  soap.  The 
amount  of  water  in  that  film  which  surrounds  the  air  inside  of  the 
bubble  is,  as  we  may  well  imagine,  very  small.  The  ordinary  soap- 
bubble  bursting  upon  this  piece  of  paper  would  hardly  leave  a 
visible  sign  of  water.  Now,  as  that  bubble  exists  as  a  bubble  the 
surface  of  that  very  small  amount  of  water  is  very  large.  It  is  the 
entire  outer  surface  of  that  bubble  and  the  entire  inner  surface, 
where  the  film  comes  in  contact  with  the  exterior  air  and  where  it 
comes  in  contact  on  the  inside  with  the  enclosed  air.  Now,  over  that 
immense  surface,  for  it  is  truly  immense  in  consideration  of  the 
small  amount  of  water,  there  is  this  contractile  force,  as  if  around 
the  bubble  there  were  stretched  a  sheet  of  rubber  constantly  drawing 
inward  to  make  that  bubble  smaller,  and  the  effort  of  that  force  of 
surface  tension  to  reduce  the  area  of  the  water  forming  the  film 


AIR-FROTH   FLOTATION 


161 


162  THE  FLOTATION  PROCESS 

of  the  bubble,  simply  pulls  it  in,  bursts  it,  reduces  it  to  a  drop, 
which  has  the  minimum  of  surface.  So  I  apprehend  that  the  reason 
the  bubbles  in  these  froths  burst  is  on  account  of  that  shrinking 
inward,  that  tendency  of  surface  tension  to  gather  the  water  into 
the  smallest  possible  compass. 

The  experts  who  have  testified  in  this  case  say  (and  their  views 
are  in  harmony  with  the  literature  on  the  subject)  that  any  substance 
which  tends  to  lower  or  lessen  the  surface  tension  of  water  tends  to 
make  the  bubbles  or  the  froth  more  persistent  or  permanent;  and 
in  view  of  what  I  have  said,  I  think  the  reason  Why  these  modifying 
agents  which  lower  the  surface  tension  of  water  also  tend  to  make 
the  froth  more  permanent  is  clear.  In  the  case  of  pure  water, 
having  a  surface  tension  which  I  think  is — well,  it  is  arbitrarily 
represented  by  some  numeral — we  can  say  1.  It  makes  no  difference. 
Now,  that  force  of  surface  tension  in  clear  water  is  strong  enough 
to  burst  these  bubbles.  It  pulls  in  and  bursts  them.  But  if  the 
water  is  modified  by  some  agent,  such  as  an  oil  in  emulsion,  or  a 
soluble  substance,  such  as  phenol  or  cresol,  that  contractile  drawing-in 
force  is  lessened,  and  therefore  the  bubble  has  greater  longevity,  can 
exist  longer,  because  there  is  hot  this  constant  pulling  in.  So,  while 
this  surface  tension  manifests  itself  in  various  ways  and  has  been 
utilized  in  various  ways,  so  far  as  this  bubble  flotation  or  froth  flota- 
tion is  concerned,  I  think  it  is  clear  why  a  lowering  of  that  surface 
tension  tends  to  permit  a  bubble  to  exist  longer.  And  all  of  the 
experts  in  this  case  are  in  perfect  agreement  that  an  insoluble  oil 
mixed  up,  or  emulsified,  lowers  the  surface  tension  in  precisely  the 
same  way  that  a  dissolved  substance  does. 

The  phenomenon  of  the  flotation  of  small  particles  upon  the  surface 
of  water,  as  upon  the  surface  of  water  in  that  glass,  has  been  referred 
to  as  surface  tension  flotation  or  skin  flotation.  That  is  a  matter  of 
arbitrary  nomenclature.  The  surface  tension  effect  does  not  enter 
into  that  effect  any  more  than  it  does  in  bubble  flotation.  This 
stretched  membrane,  as  we  picture  it,  surrounding  a  body  of  liquid 
and  tending  to  draw  it  into  a  small  compass,  also  has  the  property 
of  supporting  a  small  particle  upon  the  upper  surface  of  a  body 
of  water,  but  the  name  'surface  tension '  should  not  properly  be 
restricted  to  that  kind  of  a  flotation,  because  the  surface  tension 
phenomena  enter  into  all  flotations,  and  it  is  the  lowering  of  that 
surface  tension  that  leads  to  the  formation  of  these  froths  which 
have  more  or  less  permanency. 


AIR-FROTH    FLOTATION  163 

Besides  these  various  prior  art  patents  and  publications  that  I 
have  referred  to,  in  which  the  lowering  of  surface  tension  is  utilized 
for  the  purpose  of  giving  permanency  to  a  froth  or  a  bubble,  we 
have  other  patents,  I  believe  owned  by  the  complainants  in  this  case, 
patents  issued  to  scientific  men,  technical  men,  the  officials  connected 
with  these  companies,  in  which  they  also  explain  the  use  of  both 
soluble  and  insoluble  reagents  for  the  purpose  of  contributing 
efficiency  to  a  bubble  or  froth  process. 

Notable  among  those  is  patent  788,247,  which  is  in  evidence. 

Patent  788,247  was  granted  to  Gattermole,  Sulman,  and  Picard. 
Sulman  and  Picard  are  two  of  the  grantees  of  the  patent  in  suit. 
Now,  in  this  process — 

THE  COURT  (interposing)  :  What  is  the  date  of  that  patent? 

MR.  SCOTT  :  The  date  of  the  grant  was  April  25,  1905 ;  the  date 
of  the  application  was  March  29,  1904.  In  their  statement  of  inven- 
tion in  patent  788,247  they  say: 

"Our  process  has  for  its  object  the  separation  of  minerals  from 
silicious  or  earthy  matters  of  ores  by  means  of  soaps  or  similar 
compounds  and  is  dependent  upon  the  superior  physical  attraction 
exhibited  by  minerals  for  fatty  or  resin  acids,  or  for  certain  other 
aromatic  derivates,  such  as  phenols,  cresols,  etc.,  which  form  soluble 
salts  or  compounds  with  alkaline  hydrates. " 

Then  upon  the  first  page  of  that  same  patent  they  state : 

"The  mineral  particles  now  attached  to  or  more  or  less  coated  or 
enclosed  by  films  of  fatty  or  resin  acids  and  the  like,  are  capable  of 
being  separated  from  the  gangue  or  earthy  particles  by  various 
methods,  depending  upon  this  altered  physical  condition.  For 
example,  the  coated  mineral  particles  may  be  removed  by  generating 
gaseous  bubbles  in  the  mixture,  which  preferentially  attach  themselves 
to  the  fatty  or  similar  acid  coated  particles  and  raise  them  to  the 
surface  of  the  pulp,  whence  they  may  be  removed  by  skimming  or 
the  like. " 

There  is  a  clear  statement  of  the  use  of  soluble  agents,  the  very 
soluble  agents  which  are  mentioned  in  the  patents  here  in  suit,  with 
their  use  in  connection  with  gases  for  raising  them  to  the  surface, 
and  the  only  way  in  which  a  gas  can  function  is  as  a  bubble,  and 
this  effect  of  lowering  the  surface  tension  was  there  brought  about 
by  the  same  substances  which  are  in  use  today. 

In  patent  793,808  which  is  the  patent  disclosing  the  perforated 
spiral  coil  that  we  have  had  so  much  discussion  about,  the  patentees 
state : 

"The  present  invention  relates  to  the  concentration  of  ores  by 


164 


THE   FLOTATION    PROCESS 


separation  of  the  metalliferous  constituents  and  graphite,  carbon, 
sulphur  and  the  like,  from  the  gangue,  by  means  of  oils,  grease,  tar, 
or  any  similar  substance  which  has  a  preferential  affinity  for  metal- 
liferous matter  over  gangue." 

The  tar  there  mentioned  is  one  of  the  substances  in  use  today. 
Coal-tar  is  the  principal  source,  I  think,  of  phenol  and  cresol,  and 
it  is  used  in  a  crude  state  in  flotation  operations.  I  think  it  is  one 

No  793.808.  PATENTED  JULY  4,  1905. 

H.  L.  SDLMAN  &  H.  F.  KIRKPATRICK-PICARD. 

ORE  CONCENTRATION. 

APPUOATIOH  FILED  OCT.  5,  1903. 

3  SHEETS    SHEtP  1 


FlG.    33.      THE    PERFORATED    COIL    PATENT. 


AIR-FROTH    FLOTATION  J  65 

of  the  substances  which  the  answers  to  the  interrogatories  say  has  been 
used  by  the  Miami  company.  It  is  partially  soluble  and  partially 
insoluble.  It  is  a  mixture.  And  then  this  patent,  after  naming  these 
substances,  oil,  grease,  insoluble  substances,  and  then  mentioning  in 
the  same  breath  tar,  which  is  partially  soluble  and  partially  insoluble, 
the  same  as  is  the  frothing  agent  used  at  Miami,  after  explaining  the 
use  of  these  substances  goes  on  to  say : 

"According  to  one  method  of  carrying  out  our  invention  suitably 
crushed  ore  is  suspended  in  water.  To  this  suspension  a  proportion 
of  oil,  grease,  or  tar  (hereinafter  referred  to  as  'oil')  is  added  and 
duly  mixed  with  the  mass  by  any  suitable  means  in  quantity  insuf- 
ficient to  raise  the  oil  mineral  by  virtue  of  the  notation  power  of 
the  oil  alone.  A  suitable  gas  is  now  generated  in  or  introduced  into 
the  mixture,  such  as  air,  carbonic  acid  gas,  sulphureted  hydrogen, 
or  the  like." 

Now  here  again  we  have  a  process  in  which  a  soluble  agent  is 
used.  Tar  is  not  completely  soluble,  but  the  complainant  has  taken 
the  position,  which  I  will  accept  for  the  purpose  of  argument  at 
present,  that  if  any  constituent  of  a  substance  is  soluble,  then  the 
substance  is  a  soluble  agent  under  the  second  and  third  patents  in 
suit.  Accepting,  for  the  sake  of  argument,  this  construction  of 
these  patents,  we  have  here  disclosed,  down  to  the  minutest  detail, 
every  operation  that  is  performed  at  Miami.  We  have  tar,  a  mixture 
of  soluble  and  insoluble  agents;  we  have  the  admixture  of  that 
substance  with  the  pulp ;  we  have  the  introduction  of  that  substance 
into  a  vessel  provided  at  the  bottom  with  means  for  the  admission 
of  air ;  that  means  being  this  perforated  spiral  coil. 

2  p.  m.    Same  day. 

MR.  SCOTT  :  If  the  Court  please,  just  before  the  recess  I  was 
speaking  of  the  spiral  coil-pipe  machine,  the  perforated  spiral,  and 
had  stated  that  this  process  was  identical  with  the  operations  at 
Miami.  In  fact,  I  think  it  will  be  difficult  for  anyone  to  conceive 
of  any  different  action  on  the  part  of  air  bubbles  escaping  through 
fine  holes  in  a  metal  pipe  or  a  sheet  of  metal,  and  the  same  bubbles 
escaping  through  similar  holes  in  a  canvas  bottom.  I  do  not  think 
the  thing  needs  any  argument,  the  two  processes  are  absolutely 
identical. 

An  attempt  has  been  made  to  establish  the  appearance  of  identity 
between  that  fragile  mass  of  bubbles  which  results  from  the  Miami 
operation  and  from  the  patent  793,808,  and  the  persistent  froth  that 
results  from  the  violent  agitation  of  the  patents  in  suit. 


166  THE  FLOTATION  PROCESS 

Now  certainly  to  the  eye  there  is  no  identity  whatever.  And 
going  further,  looking  to  the  real  essence  of  the  two  operations,  we 
find  as  great  a  distinction  as  there  is  in  the  appearance.  The  agita- 
tion froth  results  from  violent  agitation  of  the  pulp,  beating  the 
air  into  very  fine  particles  and  then  bringing  the  liquid  to  rest;  as 
the  Court  has  seen  here  in  court,  when  the  agitating  mechanism 
was  stopped,  there  arises  this  persistent  froth  which  lasts  for  days. 
Even  when  shaken  in  a  bottle  in  accordance  with  the  directions  of 
the  California  Technical  Journal*,  we  showed  the  Court  a  froth  that 
had  stood  for  some  two  weeks,  I  think  Mr.  Dosenbach  testified.  That 
froth  was  so  strong  that  it  remained  as  a  bridge  across  the  bottle, 
even  after  the  water  had  evaporated  out  from  beneath  it.  I  think 
that  matter  was  called  to  the  attention  of  the  Court,  that  the  stopper 
had  been  left  out,  and  that  froth  was  so  strong  that  it  simply 
adhered  to  the  sides  of  the  bottle,  and  bridged  across  the  bottle 
without  any  support  whatever  from  below.  That  is  characteristic 
of  all  these  froths  that  are  formed  by  this  violent  agitation. 

Now  contrasting  with  that  we  have  what  was  exhibited  to 
the  Court  in  many  experiments  with  the  canvas-bottom  machine, 
our  Exhibit  53,  and  in  the  perforated  spiral-pipe  machine,  our 
Exhibit  52. 

The  first  difference  that  strikes  one  is  that  in  this  agitation  process 
the  liquid  must  be  brought  to  rest  before  the  froth  will  form.  The 
froth  will  not  form  in  the  presence  of  and  simultaneously  with  that 
violent  agitation.  The  agitating  mechanism  either  must  be  stopped, 
or  the  liquid  must  be  conducted  into  a  side  vessel  where  it  will  be 
quiet.  As  it  was  exhibited  in  court,  the  agitating  mechanism  was 
stopped,  that  being  merely  for  convenience  in  demonstration.  Both 
complainant  and  defendant  did  it  in  that  manner.  Of  course,  that 
would  make  the  operation  intermittent  if  it  was  applied  in  practice. 
It  would  simply  be  agitated,  and  stop,  and  take  off  some  froth,  and 
then  take  more  material,  and  agitate  again.  As  I  think  the  Court 
is  informed,  in  practice  the  pulp  flows  in  a  continuous  stream  through 
these  agitating  vessels  and  then  into  quiet  vessels  where  there  is  no 
agitator,  vessels  called  '  spitzkasten, '  and  the  current  as  it  flows 
along  is  so  slow  and  gentle  that  the  froth  rises  in  these  quiet  spitz- 
kasten  after  having  been  previously  agitated  in  the  adjoining  agita- 
tion vessel.  And  that  is  a  sine  qua  non  of  this  agitation  process :  that 


*  [The  California  Journal  of  Technology.    Mr.  Scott  refers  to  the  article  by 
the  three  students  abstracted  in  our  issue  of  July  31,  1915. — EDITOR.] 


AIR-FROTH    FLOTATION 


167 


the  pulp  be  subjected  first  to  violent  agitation  and  then  be  brought  to 
rest  for  this  coherent  froth  to  rise. 

Now,  it  is  equally  of  the  essence  and  vital  to  the  process  carried 
on  at  Miami  that  just  the  opposite  conditions  prevail.  In  the  process 
as  carried  on  at  Miami  the  bubbles  which  carry  the  metal  concentrate 
to  the  surface  can  rise  and  can  exist  only  in  the  presence  of  these 

Ho,  835,120.  PATENTED  NOV.  6,  1906. 

H.  L.  SULMAN,  H.  F.KIRKPATRICK-PICARD  &  J.  BALLOT. 

ORE  CONCENTRATION. 

APPLICATION  FILED  MAY  29,  1905. 

»  SHEETS-SHEET  1. 


FlG.  34.      DIAGRAM  ACCOMPANYING  THE  MINERALS  SEPARATION  BASIC  PATENT. 


168  THE  FLOTATION  PROCESS 

incoming  streams  of  air  from  the  bottom  of  the  vessel.  The  com- 
plainant has  contended  that  the  mere  gentle  entrance  of  these  bubbles 
at  the  bottom  of  the  vessel  is  the  equivalent  of  the  violent  agitation 
which  forms  a  vital  and  essential  element  in  the  process  of  the 
patents  in  suit. 

There  again  to  the  eye  there  is  no  similarity  and  no  equivalency. 
In  the  agitation-froth  process  of  the  patents  in  suit — and  they  are 
all  alike  in  the  mechanical  treatment  of  the  pulp  by  agitation — we 
have  a  mass  of  water  that  is  beaten  into  a  perfect  vortex  or  maelstrom, 
as  violent  a  movement  as  we  can  conceive  of ;  whereas  in  the  Miami 
process  where  the  air  is  admitted  through  a  permeable  bottom,  we 
have  no  more  agitation  than  one  would  observe  in  a  glass  of  charged 
liquor,  soda  water,  or  champagne.  There  are  simply  the  rising 
bubbles  coming  through  the  liquid.  So  far  there  is  no  similarity. 

Look  at  the  principle  of  the  thing.  There  is  an  even  greater 
dissimilarity.  In  the  first  place,  as  I  have  just  stated,  in  the  agitation- 
froth  process  the  froth  or  bubbles  can  rise  only  after  the  agitation 
has  stopped,  or  after  the  pulp  has  been  conducted  to  a  quiet  place 
away  from  the  agitating  vessel. 

In  the  Miami  process  the  moment  the  influx  of  air  stops — and 
air  is  what  is  contended  to  be  the  equivalent  of  the  agitation,  that 
is,  the  incoming  stream  of  air — the  minute  that  stops  in  the  Miami 
process,  the  entire  body  of  bubbles  carrying  the  concentrate  collapses, 
and  I  think  your  Honor  has  a  vivid  impression  of  that  demonstration 
in  which  Mr.  Yerxa  and  Mr.  Hunt  first  turned  on  the  air  in  that 
spiral-coil  machine,  and  in  the  canvas-bottom  machine,  and  built  up 
this  mass  of  bubbles,  and  then  suddenly  turned  the  air  off,  whereupon 
this  all  dropped. 

Now,  looking  at  the  matter  of  equivalency,  it  seems  to  be  an 
impossible  construction  of  the  facts  and  law  to  urge  that  the  incoming 
air-streams  in  the  bottom  of  the  permeable-bottom  cell,  whether  it 
be  the  spiral  pipe  or  the  canvas  bottom,  is  the  equivalent  of  the 
agitation,  when  their  action  is  precisely  opposite  in  respect  to  the 
formation  of  the  froth.  In  one  case  the  froth  forms  only  when 
the  agitation  ceases.  In  the  other  the  floating  or  rising  bubbles  exist 
only  while  the  so-called  agitation  is  going  on.  The  principle  of  the 
two  things  is  as  different  as  the  manifestation  of  that  principle.  The 
manifestation  differs  in  this  respect  that  I  have  pointed  out.  In 
one  the  froth  rises  when  the  agitation  stops.  In  the  other  the 
bubbles  can  rise  only  when  this  so-called  agitation  is  going  on. 

Now  as  to  the  principle.     The  two  processes  attack  the  problem 


AIR-FROTH    FLOTATION  169 

in  completely  different  ways.  In  the  agitation-froth  process  the 
thought  is  so  to  treat  this  pulp  by  violent  agitation  that  a  froth  will 
form  and  exist  after  agitation,  that  froth  to  be  of  so  permanent  and 
lasting  a  character  that  it  can  be  manipulated,  can  be  floated  or 
skimmed  off,  as  the  Court  has  seen  witnesses  do  in  this  case.  The 
idea  there  was  by  this  agitation  to  effect  a  separation  more  or  less 
permanent  between  the  gangue  and  the  concentrate,  to  get  the  gangue 
at  the  bottom  and  the  concentrate  at  the  top — to  stratify  them,  as 
it  were.  We  have  the  two  strata  with  an  intervening  stratum  of 
water.  And  then  to  take  off  that  froth  in  any  way  which  may  be 
convenient,  either  by  simply  flowing  off  or  by  skimming,  as  has 
been  explained  by  complainants'  witnesses  in  that  instance  where 
they  had  a  revolving  paddle  something  after  the  fashion  of  the 
stern-wheel  on  some  of  the  river-steamers.  That  paddle  would  revolve 
and  scrape  off  this  froth. 

In  the  Miami  process  the  mode  of  attack  upon  the  problem  is 
completely  different.  There  is  no  idea  in  the  Miami  process  of 
stratifying  these  materials  and  making  a  permanent  float,  which  can 
be  scraped  off  or  floated  off.  The  thought  there,  and  the  process  as 
actually  carried  out,  is  to  admit  at  the  bottom  of  the  vessel  containing 
the  pulp  with  the  agent  that  is  used,  a  stream  of  air  bubbles  which 
act,  as  Dr.  Liebmann  has  said,  simply  like  an  upcast.  These  air 
bubbles,  rising  by  the  force  of  gravity  through  the  water,  collect 
the  mineral  particles  by  reason  of  the  fact  that  they  do  collect  them. 
That  is  about  all  that  we  can  say,  that  the  mineral  particles  adhere 
to  these  bubbles  while  the  gangue  does  not. 

Then  the  bubbles  come  to  the  surface  of  the  water  and  break 
almost  instantly.  There  is  a  constant  succession  of  breaking  bubbles, 
but  the  influx  of  air  at  the  bottom  of  this  vessel  manufactures  these 
bubbles  at  a  slightly  more  rapid  rate  than  they  break,  and  for  that 
reason  the  upper  layer  of  bubbles  is  overflowed  from  the  top  of  the 
vessel  and  saved,  with  their  burden  of  mineral.  The  only  reason 
that  the  Miami  process  is  a  success,  or  that  the  process  of  patent 
793,808  is  a  success,  is  that  it  is  possible  by  these  rising  bubbles  to 
make  the  bubbles  a  little  faster  than  they  break.  If  they  broke  as 

MR.  SCOTT  :    Up  to  the  top. 

THE  COURT  :    Up  to  the  surface,  or  above  the  surface  ? 

MR.  SCOTT  :    Precisely. 

THE  COURT:  Now,  where  in  the  complainant's  process  does  the 
bubble  attach  itself  to  the  mineral — below  the  surface  or  above  ? 

MR.  SCOTT  :    I  think  that  must  be  below  the  surface,  too. 


170  THE  FLOTATION  PROCESS 

fast  as  they  were  made,  we  would  never  have  any  appreciable  amount 
of  bubbles  on  top.  They  would  simply  break,  each  one  in  time  for 
the  next  one  to  come  up ;  but  as  it  is  there  is  a  small  interval  of 
time  before  they  break,  and  more  bubbles  are  being  formed  at  a 
rate  so  rapid  that  some  of  those  bubbles  are  raised  to  the  top  and 
carried  over  the  top  before  they  have  broken,  and  that  is  the  only 
reason  that  it  is  possible  to  concentrate  ores  in  that  way. 

The  frothing  process,  on  the  other  hand,  is  not  dependent  upon 
any  such  principle  at  all.  The  thing  is  simply  agitated  violently, 
and  when  the  agitation  stops,  this  froth  rises  and  floats  much  the 
same  as  a  board  would.  It  may  not  be  as  long-lived  as  a  piece  of 
wood,  but  it  lasts  for  weeks,  and  it  simply  rises  there  and  floats. 
Speaking  with  regard  to  the  purpose  of  concentration,  it  is 
permanent,  within  the  limitations  that  permanency  is  necessary  or 
desirable. 

Now  in  view 

THE  COURT:  Let  me  see  if  I  get  your  idea.  Do  you  draw  a 
distinction  between  a  process  which  results  in  the  formation  of  what 
is  termed  a  permanent  froth,  and  a  process  in  which  the  bubbles  come 
up  in  rapid  succession,  but  not  in  such  quantities  or  in  such  close 
proximity  as  to  form  a  permanent  froth,  but  as  soon  as  they  get  to 
the  surface  they  float  away;  is  that  what  you  mean? 

MR.  SCOTT  :  They  float  over,  if  we  get  them  over  before  they 
break.  It  is  a  kind  of  a  race. 

THE  COURT:  If  you  get  them  over  before  they  break?  But 
suppose  they  break  before  you  get  them  over,  what  becomes  of  the 
mineral ? 

MR.  SCOTT  :  Then,  as  is  shown  in  these  demonstrations,  if  they 
do  break,  the  mineral  drops,  and  it  is  caught  by  the  bubbles  below. 

THE  COURT  :    And  brought  up  again  ? 

MR.  SCOTT  :  And  brought  up  again.  The  bubbles  must  be  brought 
up  fast  enough  so  that  it  will  gradually  be  raised. 

THE  COURT  :    That  is,  above  the  surface, 

MR.  SCOTT  :  Yes.  There  must  be  new  bubbles  coming  fast  enough 
so  that  it  is  gradually  carried  up  over. 

THE  COURT:    And  they  float  off? 

MR.  SCOTT  :    And  finally  float  off. 

THE  COURT  :  That  is  what  I  meant.  I  did  not  express  it  in  that 
way.  You  expressed  it  in  two  stages,  a  first  mass  of  bubbles  and  a 
succeeding  mass  of  bubbles,  but  that  was  what  was  in  my  mind. 

MR.  SCOTT  :    The  same  idea,  I  think. 


AIR-FROTH    FLOTATION  171 

THE  COURT  :     That  there  is  no  permanence  ? 

MR.  SCOTT  :  No  permanence  in  the  bubble  process  at  Miami. 
Now,  if  the  Court  remembers  the  mass  of  bubbles  was  probably  about 
6  inches  high  above  the  water,  as  I  remember. 

MR.  KENYON:    Ten  or  twelve  inches  high. 

MR.  SCOTT  :  Ten  or  twelve  inches  high.  It  was  quite  high.  Now, 
if  a  particle  should  be  allowed  to  drop  by  reason  of  the  bubble 
breaking,  it  would  be  caught  on  a  bubble  below,  and  thus  constantly 
raised  up  by  new  bubbles  coming  into  the  bottom,  so  that  it  is,  as 
you  might  say,  a  case  of  stepping  back  an  inch  and  going  forward 
two  inches,  and  gradually  getting  over,  despite  the  breaking  of  the 
bubbles. 

The  term  'flotation7  seems  inaccurate  as  applied  to  this  Miami 
process.  In  the  agitation-froth  process,  after  the  agitation  is  stopped, 
this  froth  actually  does  float.  It  will  float  for  hours,  and  days,  and 
weeks,  and  stay  on  the  top  of  the  water;  but  in  the  Miami  process, 
as  soon  as  the  incoming  current  of  air  stops,  everything  drops,  and 
we  have  the  clear  water-surface  on  the  top  of  the  cell.  Now,  that 
demonstrates  absolutely  that  that  mass  of  bubbles  several  inches 
deep,  which  we  see  in  the  Miami  process  operation,  or  that  of  the 
patent  793,808,  is  not  really  floating.  It  is  held  up  there  by  the 
current  of  air,  which  holds  it  in  place.  That  current  of  air  not  only 
manufactures  these  bubbles  so  fast  that  we  have  that  mass  of  bubbles 
there,  but  it  actually  holds  them  up  in  position,  and  the  minute  the  air 
is  turned  off  everything  drops.  The  mineral  goes  right  to  the  bottom, 
and  the  bubbles  break.  So  that  instead  of  a  floating  mass  of 
concentrate,  it  seems  to  me  that  it  is  best  described,  as  I  think  I  did 
once  before  in  opening  the  case,  by  saying  that  this  Miami  operation 
is  similar  to  these  devices  we  have  seen,  where  a  stream  of  air  is 
blown  out  of  a  pipe  and  a  ball  floats  above  it.  The  minute  the  stream 
of  air  is  turned  off  the  ball  drops.  In  popular  language,  we  may 
say  that  that  ball  is  floating  in  the  air,  but  obviously  that  is  a 
misnomer,  if  we  attach  any  exact  meaning  to  our  words. 

Now,  the  Miami  process  is  analogous  to  this  ball  held  up  on  that 
stream  of  air.  The  agitation-froth  process  is  the  ball  floating  in 
the  water.  The  two  things  operate  upon  absolutely  different 
principles,  and  the  difference  is  so  great  that  it  cannot  escape  anyone's 
notice. 

Dr.  Liebmann  has  characterized  this  Miami  cell,  or  Callow  cell, 
as  he  calls  it,  as  an  upcast,  and  the  figure  of  speech  is  very  happy. 
We  took  an  ordinary  upcast  with  water,  such  as  that  which  was 


172  THE  FLOTATION  PROCESS 

used  for  separating  the  Cattermole  granules;  and  the  Court  will 
well  remember  that  the  mixture,  the  granules  and  gangue,  was 
brought  downward  into  a  pipe,  and  water  was  flowing  upward  in  the 
pipe,  and  that  upward  stream  of  water  carried  off  the  light  tailing, 
and  the  heavy  granules  sank  to  the  bottom.  Now,  'upcast'  is  the 
term  that  is  ordinarily  used,  and  the  action  which  takes  place  in  this 
Miami  process  is  absolutely  analogous  to  that.  It  is  not  a  floating 
operation.  It  is  an  operation  in  which,  in  a  rising  current  of  air, 
gravity  is  strong  enough  to  pull  some  of  the  particles  down,  but  the 
other  particles  are  of  such  gravity  and  shape  that  the  rising  current 
of  air  carries  them  up  against  the  force  of  gravity. 

THE  COURT  :  Let  me  ask  you,  where  is  the  gangue  separated  from 
the  metal? 

MR.  SCOTT  :    In  the  Miami  process  ? 

THE  COURT:    Yes. 

MR.  SCOTT  :  The  gangue  comes  out  at  the  bottom  and  the  mineral 
is  carried  over  the  top. 

THE  COURT  :    Yes.    How  is  that  the  result  of  this  upcast  ? 

MR.  SCOTT :    Of  air? 

THE  COURT:  What  is  it  that  separates  the  gangue  from  the 
particles  ? 

MR.  SCOTT :  The  rationale  of  the  thing  is  evidently  this:  We 
have  in  this  cell,  or  tank  with  the  porous  bottom,  water  carrying  in 
suspension  both  gangue  particles  and  mineral  particles,  and  the 
mixture  has  been  treated  with  some  of  these  agents — tar,  or  coal 
tar,  or  what  not — mixed  up  with  it.  In  the  first  place,  those  air 
bubbles  attract  to  themselves  the  mineral  particles  and  do  not  attract 
the  gangue  particles;  so  that  at  that  stage  of  the  operation  we  have 
in  the  water  a  series  of  bubbles  with  the  mineral  particles  sticking 
to  them,  and  we  have  the  gangue  particles  free  in  the  water  itself. 
Now,  those  bubbles  rise,  of  course,  by  gravity  and  carry  with  them 
those  mineral  particles.  The  combination  of  the  bubble  and  the 
mineral  particle  is  together  lighter  than  water,  so  it  goes  to  the  top. 

THE  COURT  :    I  understand. 

MR.  SCOTT  :  And  the  gangue  particle  has  had  no  assistance  what- 
ever from  the  air.  It  is  still  heavier  than  water,  the  way  it  always 
was,  and  it  goes  to  the  bottom. 

THE  COURT:  I  understand,  then,  that  in  the  Miami  process  the 
bubble  attaches  itself  to  the  mineral  below  the  surface. 

MR.  SCOTT  :    Below  the  surface,  yes. 

THE  COURT  :     And  carries  the  mineral — 


AIR-FROTH   FLOTATION  173 

THE  COURT  :     And  it  carries  it  up,  does  it  ? 

MR.  SCOTT  :    It  carries  it  up  to  the  top. 

THE  COURT:  Is  it  not  pretty  much  a  question  of  froth,  rather 
than  of  concentration — the  difference  between  the  two  processes?  I 
understand  that  the  purpose  of  the  patents  is  to  effect  not  a  froth, 
but  a  concentration. 

MR.  SCOTT  :    Precisely. 

THE  COURT  :     A  separation  ? 

MR.  SCOTT  :    Precisely. 

THE  COURT  :  Now,  you  may  assume  that  I  do  not  know  anything 
about  this.  I  want  to  have  it  put  to  me  as  plainly  as  you  can  express 
yourself.  What  is  the  distinction  in  principle  between  those  two 
processes?  You  have  explained  the  difference  in  point  of  actual 
operation.  Now,  what  is  the  distinction  in  principle,  when  it  comes 
to  the  formulation  of  any  principle,  between  these  two  operations, 
as  bearing  upon  the  question  of  the  separation  and  saving  of  the 
metaljDarticles  ? 

MR.  SCOTT  :  The  broad  principles  are  the  same  in  both.  In  both 
we  have  the  pulp,  consisting  of  ore  held  in  suspension  in  water.  In 
both  the  water  is  modified  to  lower  its  surface  tension.  In  both 
the  buoyancy  comes  from  air  bubbles.  The  difference  comes  after 
the  air  bubbles  have  attached  themselves  to  the  mineral  particles. 
In  the  agitation-froth  process  the  air  is  beaten  into  very  minute 
bubbles,  and  when  they  rise  with  these  mineral  particles  they  form 
this  permanent  froth.  The  permanent  froth  is  then  floated  off  or 
skimmed  off.  Now,  in  the  Miami  process  there  is  no  beating  up  of 
the  liquid,  of  the  pulp.  The  bubbles  are  larger  and  more  fragile, 
and  instead  of  forming  a  permanent  froth,  which  will  float,  the  thing 
is  simply  pushed  off  by  the  current  of  air.  The  basic  principles  are 
the  same  in  both  of  them.  The  method  practised  at  Miami  is  the 
older  of  the  methods.  It  is  the  method  of  the  patent  793,808,  with 
the  perforated  spiral  coil. 

Now,  speaking  so  far  as  patents  go,  departing  from  the  Court's 
question  as  to  the  general  principle  of  the  thing,  which  is  identical 
up  to  the  point  I  have  explained — departing  from  broad  explanations 
and  approaching  it  from  the  patent  side  purely,  the  patents  in  suit 
must  necessarily,  if  they  have  any  validity  whatever,  be  restricted 
to  this  permanent  froth  formed  by  this  mechanical  agitation,  or  they 
must  confessedly  be  invalid  by  the  prior  existence  of  the  perforated 
coil-pipe  machine. 

THE  COURT  :    Let  me  ask  you  another  question. 


174  THE  FLOTATION  PROCESS 

MB.  SCOTT  :     Certainly,  I  am  very  glad  to  have  you  do  so. 

THE  COURT  :    When  was  the  perforated-coil  machine  first  used  ? 

MR.  SCOTT  :    As  far  as  the  record  in  this  case  shows — 

THE  COURT:    I  mean  with  respect  to  the  first  patent  in  suit. 

MR.  SCOTT  :  The  date  of  the  application  was  about  a  couple  of 
years  before,  and  I  think  the  patent  was  granted  about  a  month 
before  the  application  in  this  country.  I  will  give  you  the  exact 
date.f 

THE  COURT  :    I  mean,  was  it  before  ? 

MR.  SCOTT  :    Oh,  absolutely. 

THE  COURT  :    Before  the  first  patent  in  suit  ? 

MR.  SCOTT  :    Before  the  first  patent  in  suit. 

THE  COURT:  Now,  let  me  ask  you,  what  were  the  ingredients 
that  were  used,  and  what  proportions  were  used  ? 

MR.  SCOTT  :  In  this  patent  the  ingredients — and,  of  course,  in 
all  of  these — are  the  ore-pulp  in  the  first  place,  the  water  and  the  ore. 

THE  COURT  :    Yes. 

MR.  SCOTT  :  And  the  ingredients  for  effecting  bubble  formation 
in  this  patent  793,808  are  oils,  grease  and  tar,  or  any  similar  substance, 
which  has  a  preferential  affinity  for  metalliferous  matter  over  gangue. 

THE  COURT  :    And  in  what  proportions  ? 

MR.  SCOTT  :  The  proportions  are  stated  in  the  patent  in  this 
language — there  are  no  figures — in  line  89  of  the  first  page  of  the 
patent : 

"We  have  also  found  that  a  particle  of  metalliferous  mineral,  if 
coated  with  a  minute  film  of  oil,  grease  or  the  like*  *  *  *  ' 
And  so  forth.  That  expression,  "minute  film"  certainly  gives  us 
indication  of  a  very  small  quantity,  because  the  word  'film'  without 
any  qualification  whatever,  conveys  to  the  mind  the  idea  of  a  very 
small  amount;  and  when  you  say  "a  minute  film"  we  are  getting 
about  the  strongest  expression  of  the  necessity  of  a  small  quantity 
that  words  can  convey. 

There  is  one  other  place  in  this  patent  where  I  think  the  quantity 
is  similarly  characterized. 

MR.  SHERIDAN  :    At  the  top  of  page  2. 

MR.  SCOTT  :  "A  small  proportion  of  oil, ' '  following  the  ' ' minute 
film." 


t[The  coil-pipe  patent  (No.  793,808)  is  dated  July  4,  1905,  but  the  applica- 
tion was  filed  on  October  5,  1903.  On  the  other  hand  the  basic  agitation-froth 
patent  No.  835,120  is  dated  November  6,  1906,  while  application  for  it  was 
made  on  May  29,  1905. — EDITOR.] 


WHY    DO    MINERALS   FLOAT?  175 

This  brings  us,  of  course,  to  what  I  regard  as  the  only  real  ques- 
tion in  the  case,  and  that  is  as  to  whether  there  is  any  distinction  in 
principle  between  the  froth  which  is  formed  with  a  very  small  quantity 
of  oil  and  one  which  is  formed  with  a  larger  quantity;  in  other 
words,  whether  there  is  a  difference  between  an  air-froth  and  an 
oil-froth  or  emulsion.  The  first  patent  in  suit,  835,120,  states  that  less 
than  1%  of  oil  is  used;  and  then  in  describing  the  action  of  that  oil  it 
states  that  it  coats  the  mineral  particles.  Well,  they  cannot  be  coated 
otherwise  than  by  a  minute  film.  The  descriptive  language  is  pre- 
cisely the  same,  and  then,  as  shown  by  the  demonstrations  in  this 
Court,  we  have  produced  the  same  result  ocularly,  and  metallurg- 
ically,  with  these  large  quantities  of  oil  as  with  the  minute  quantity. 


WHY  DO  MINERALS  FLOAT? 

By  OLIVER  C.  RALSTON 
(From  the  Mining  and  Scientific  Press  of  October  23,  1915) 

*I  was  very  much  interested  in  reading  an  article  by  Charles  T. 
Durell,  appearing  in  the  Mining  and  Scientific  Press  of  September  18, 
under  the  caption  '  Why  Is  Flotation  ? '  However,  I  find  myself  unable 
to  agree  with  Mr.  Durell's  line  of  argument,  and  for  the  following 
reasons : 

In  the  first  place  I  believe  that  Mr.  Durell  has  used  loosely  some 
rather  obscure  scientific  terms  which  may  cause  unnecessary  confusion 
to  anyone  not  thoroughly  familiar  with  the  physical  chemistry  in- 
volved. The  term 'nascent  gas' is  especially  open  to  criticism.  Doubt- 
less Mr.  Durell  means  the  dissolved  gas  that  can  be  liberated  from  the 
water,  but  that  is  hardly  the  ordinary  sense  of  the  term,  and  many 
modern  physical  chemists  will  object  to  the  use  of  the  word  *  nascent' 
under  any  conditions  whatever,  or  even  refuse  to  recognize  it,  in  spite 
of  the  old  ideas  that  grew  up  around  it.  However,  it  may  be  that 
' nascent'  is  a  good  term  to  use  here  in  a  figurative  sense.  Another 
term  used  by  Mr.  Durell  and  to  which  an  objection  might  be  raised 
is  the  word  'occlusion'  as  applied  to  the  gases  held  by  minerals. 
Mineralogists  have  long  used  this  term  rather  loosely,  but  Mr.  Durell 


*Communicated  by  D.  A.  Lyon,  metallurgist  in  charge  of  Utah  Experi- 
ment Station,  U.  S.  Bureau  of  Mines  and  Department  of  Metallurgical 
Research  of  University  of  Utah,  Salt  Lake  City,  Utah.  O.  C.  Ralston, 
assistant  metallurgist. 


176  THE  FLOTATION  PROCESS 

does  not  seem  to  have  taken  it  up  in  the  same  sense.  As  I  understand 
it,  there  are  three  ways  other  than  in  visible  openings  by  which  gases 
can  be  held  in  solids  j1  these  are : 

1.  In  solid  solution,  in  the  same  way  that  gases  can  be  held  in 
liquid  solutions. 

2.  In  surface  adsorption,  where  the  layer  of  gas  immediately  in 
contact  with  the  solid  is  found  to  be  more  or  less  tightly  held  by  some 
force  of  attraction,  unnamed,  and  is  hence  considerably  compressed. 

3.  In  occluded  form.     This  is  a  term  the  meaning  of  which  has 
been  much  disputed ;  it  is  often  used  in  the  sense  of  one  or  the  other 
of  the  terms  above  mentioned.     Of  late  there  has  been  a  tendency  to 
call  occluded  gas  any  gas  that  seemingly  is  held  in  some  manner  dif- 
ferent from  that  designated  by  either  of  the  other  two  terms,  and  in 
a  manner  not  exactly  understood.     An  example  is  found  in  certain 
substances  that  are  known  to  be  finely  porous  and  that  seem  to  hold 
gases  in  neither  solid  solution  nor  surface  adsorption.     Charcoal  is 
such  a  substance.     Possibly  these  have  pores  of  such  small  diameter 
that  they  are  of  the  same  order  of  magnitude  as  the  thickness  of  the 
adsorbed  layer  of  gas,  so  that  most  of  the  gas  held  in  them  is  present 
in  a  highly  compressed  condition.     Charcoal  absorbs  so  much  C02, 
for  instance,  that  at  ordinary  temperatures  the  volume  of  C02  held 
is  enough  to  fill  the  known  pore-space  at  a  pressure  sufficient  to 
liquify  it.2 

There  doubtless  are  very  fine  openings  in  our  crystalline  sulphides, 
and  they  admittedly  do  hold  some  occluded  gas,  but  good  cases  of 
occlusion  have  been  found  thus  far  only  in  amorphous  substances  like 
charcoal,  hair,  wool,  glue,  meerschaum,  starch,  etc.  This  fact  tends 
to  cast  a  doubt  upon  Mr.  Durell's  hypothesis  that  the  occluded  gas  in 
the  flotative  minerals  plays  an  active  part  in  the  attachment  of  gas 
bubbles  to  the  surface  of  the  mineral. 

Another  physical  fact  that  casts  further  doubt  on  this  hypothesis 
is  that  occluded  gases  (and  dissolved  gases  as  well)  are  liberated  from 
the  substances  occluding  them  only  with  difficulty;  the  last  traces  of 
them  are  still  held  even  when  the  substance  is  placed  in  a  high  vacuum 
and  heated  to  a  considerable  degree.  It  is  as  though  the  molecules  of 
the  gas  were  diffusing  out  through  very  small  clogged  pores.  How 
this  tightly-held  gas  could  be  liberated  fast  enough  to  compare  with 
the  exceedingly  short  time  which  it  takes  to  accomplish  flotation  of  a 


^Philosophical  Magazine,  Vol.  XVIII,  page  916,  1909. 

2See  the  researches  of  Sir  James  Dewar  on  charcoal,  published  in  various 
volumes  of  Chemical  News. 


WHY    DO    MINERALS    FLOAT?  177 

sulphide  particle,  is  difficult  to  explain  physically.  Mr.  Durell  has 
further  supposed  that  there  is  an  osmotic  travel  of  ions  from  the  water 
solution,  in  which  the  ore  pulp  is  made  up,  directly  into  the  fine  open- 
ings of  the  mineral  particles.  The  surface  of  the  particle  acts  as  a 
septum  and  at  the  same  time  the  molecules  of  the  gas  diffuse  out  and 
join  the  air  from  the  solution,  forming  a  bubble  that  floats  the  min- 
eral. At  the  present  time  I  cannot  see  my  way  to  accept  Mr.  Durell's 
supposition.  Briefly  stated,  then,  Mr.  Durell's  hypothesis  is  that 
"nascent"  gas  from  the  water  and  "dissolved"  gas  from  the  solid 
meet  and  collect  at  the  surface  of  the  solid  until  a  bubble  large  enough 
to  lift  the  particle  is  formed,  while  the  purpose  of  an  oil  is  to  form 
a  persistent  froth  so  that  the  particle  will  not  be  dropped  back  into 
the  pulp.  I  am  of  the  opinion  that  all  the  phenomena  cited  by  Mr. 
Durell  constitute  no  proof  of  any  part  of  his  hypothesis,  but  only 
furnish  the  basis  for  an  inference  that  such  could  be  the  case.  Whether 
it  is  possible  to  get  flotation  from  water  containing  no  dissolved  gases 
and  with  minerals  that  have  been  treated  for  the  removal  of  their 
occluded  gases,  no  one  knows.  Possibly  Mr.  Durell  is  right  when  he 
says  that  "this  phenomenon  is  worthy  of  investigation,"  but,  on  the 
other  hand,  I  believe  that  flotation  can  be  explained  more  satisfactorily 
than  by  the  conjecture  that  well  crystallized  minerals,  such  as  the 
metallic  sulphides,  contain  important  amounts  of  either  occluded  or 
dissolved  gases,  and  that  they  contain  these  gases  in  any  greater 
amount  than  do  the  equally  well  crystallized  gangue-minerals,  such 
as  quartz  and  feldspar.  That  surface  films  of  adsorbed  gas  or  air 
exist  and  may  be  of  great  importance,  I  firmly  believe,  but  there  is 
little  evidence  of  any  great  difference  in  the  amount  of  this  gas  on 
gangue  and  on  flotative  minerals. 

As  I  understand  Mr.  Durell,  the  sole  use  of  the  oil  in  froth-flota- 
tion is  the  formation  of  a  tougher  liquid  film  around  the  bubbles  of 
air,  so  that  the  resulting  froth  is  more  persistent.  Mr.  Rickard3  has 
pointed  out  that  various  writers  have  continually  made  the  statement 
that  the  surface  tension  of  water  is  increased  by  the  addition  of  the 
oil,  while  -as  a  matter  of  fact  it  is  decreased.  This  fact  Mr.  Durell 
acknowledges,  and  yet  he  states  that  because  the  surface  tension  of 
the  water  is  decreased,  the  tendency  to  float  is  likewise  decreased.  He 
implies  that  the  reason  is  because  the  bubbles  burst  more  easily.  This 
seems  strange,  but  in  the  absence  of  further  data  we  can  let  it  pass. 
My  main  comment  is  that  while  Mr.  Durell  believes  that  the  only 
function  of  oil  is  the  toughening  of  the  surface  film,  we  are  not  sure 


.  &  8.  P.,  Sept.  11,  1915,  page  383. 


178  THE  FLOTATION  PROCESS 

that  such  is  the  case.  His  hypothesis  about  " nascent"  gas  and 
''occluded"  gas  does  not  require  the  presence  of  oil;  hence  he  has  had 
to  explain  the  use  of  oil  or  abandon  the  hypothesis. 

Although  I  consider  that  Mr.  Durell  should  be  applauded  for  his 
courage  in  putting  forward  a  hypothesis  concerning  a  subject  that 
has  been  of  so  empirical  a  nature  up  to  date,  nevertheless  I  have  felt 
the  necessity  for  challenging  Mr.  Durell's  hypothesis  and  of  taking 
the  liberty  of  advancing  what  seems  to  me  to  be  a  better  one. 

There  are  two  such  hypotheses  which  seem  to  be  equally  possible 
and  it  is  not  certain  but  that  the  two  simply  cover  parts  of  a  greater 
fact.  One  hypothesis  can  be  stated  in  terms  of  the  inter-facial  ten- 
sions involved,  and  the  other  in  terms  of  the  electric  charges  residing 
on  suspended  particles. 

The  first  hypothesis  is  based  on  some  academic  work  done  by 
Reinders.4  He  based  his  work  on  some  equations  that  Clerk  Maxwell5 
had  derived  from  fundamental  thermo-dynamic  laws,  leading  up  to  a 
certain  set  of  inequalities  between  inter-facial  tensions  of  the  phases 
involved.  By  'inter-facial  tension'  I  mean  the  state  of  strain  existing 
at  the  zone  of  meeting  of  any  two  dissimilar  phases.  The  surface  of 
water  in  contact  with  air  is  under  a  strain  which  we  call  'surface 
tension/  so  that  this  surface  acts  like  a  tightly-stretched  rubber  mem- 
brane. Likewise  the  inter-face  between  a  solid  and  water  and  between 
a  solid  and  air  or  between  oil  and  water  is  under  a  similar  strain. 
Allusion  has  been  made  already  to  the  surface  adsorption  of  air  on 
solids.  The  inter-facial  tensions  of  many  pairs  of  liquids  are  known, 
as  well  as  the  surface  tensions  of  all  manner  of  liquids  in  contact  with 
all  manner  of  gases.  However,  the  inter-facial  tensions  of  solids  in 
contact  with  liquids  have  never  been  studied  thoroughly  on  account  of 
the  difficulty  of  getting  measurements  that  mean  anything.  Reinders 
deduced  the  following  inequalities  as  applying  to  the  case  where  a 
powder,  or  the  particles  of  a  colloid,  is  suspended  in  a  liquid  to  which 
is  added  a  second  liquid  that  is  immiscible  with  the  first.  Let  us 
assume  that  the  first  liquid  is  water  and  the  second  oil,  then  expressing 
the  inter-facial  tension  between  the  solid  and  water  as  T(SjW),  the 
tension  between  water  and  oil  as  T(W)0),  and  the  tension  between  the 
solid  and  oil  as  T(B>0),  Reinders  stated  that: 

If  T(8>0)  >  T(W(0)  +  T(S>W)  the  solid  powder  will  remain  suspended 
in  the  water. 


iKolloid  Zeitschrift,  13:235  and  Ghent.  WeekWad,  10:700. 
^Encyclopedia  Britannica,  on  'Capillarity.' 


WHY   DO    MINERALS    FLOAT?  179 

If  T(W,S)  >  T(W)0)  +  T(0)S)  the  solid  will  leave  the  water  and  go 
into  the  layer  of  oil. 

If  T(W>0)  >  T(S,W)  -f-  T(S)0),  or  if  none  of  the  three  tensions  is 
greated  than  the  sum  of  the  other  two,  the  solid  particles  will  collect 
at  the  boundary  between  the  oil  and  water. 

It  hardly  needs  to  be  said  that  here  we  find  something  very  close 
to  the  conditions  obtaining  in  the  flotation  process.  In  fact,  the  old 
Elmore  bulk-oil  flotation  method  fulfills  exactly  the  conditions  that 
Reinders  had  in  mind.  Below  are  given  some  tables  of  results  obtained 
by  both  Reinders  and  Hoffmann6  in  an  experimental  way,  by  sus- 
pending a  definite  powdered  solid  in  water,  adding  a  second  im- 
miscible liquid,  and  shaking.  The  letter  w  means  that  the  powder 
remained  in  the  water ;  the  letter  o  means  that  the  powder  went  into 
the  oil  layer;  the  letter  s  means  that  the  powder  went  to  the  surface 
separating  the  oil  from  the  water,  and  symbols  like  s(w)  or  s(o) 
mean  that  there  was  a  good  deal  more  of  the  powder  in  the  inter-face 
than  in  the  bracketed  phase.  Similar  results  were  obtained  with 
colloidal  solutions. 

TABLE  OP  REINDERS'  RESULTS 

Paraffin  Amyl 

Water  and  oil.  alcohol.  CC14.      Benzene.  Ether. 

Kaolin    w  w(s)  w(s)  w  w(s) 

CaF2 ws  ws  w(s)  w(s)  w(s) 

Gypsum    w  ws      .  w  sw  ws 

BaSO4   w(s)  ws  ws  sw  ws 

Magnesium    ws  ws  ws  ws  ws 

PbO    s  s  SWL_  s  sw 

Malachite  so  s  s  s  sw 

ZnS s  s  s  s  sw 

PbS    so  so  s  s  s 

HgI2 so  s  s  s  s 

Carbon    so  s  s  s  s 

Selenium    so  so  so  s  s 

Sulphur    so  so  o  (s)  so  s 

Hoffmann  worked  a  great  deal  with  chemical  precipitates  and  other 
artificially  prepared  products.  However,  the  laboratory  method  in- 
volved ought  to  be  good  in  the  study  of  flotation  processes  for  a  pos- 
sible method  of  floating  oxidized  minerals.  Then  it  might  be  possible 
to  convert  a  successful  bulk-oil  process  into  a  frothing  process  in  the 
same  way  as  the  old  Elmore  bulk-oil  method  went  through  the  stage 
of  granulation  and  classification  to  a  final  frothing  process  such  as  we 


*Zeit.  physik.  Chem.,  83:409,  1913. 


180 


THE   FLOTATION   PROCESS 
TABLE  OF  HOFFMANN'S  RESULTS 


Chloro- 

Butyl 

Kero- 

Amyl 

Paraffin 

Water  and 

Ether. 

form. 

alcohol. 

Benzene. 

sene. 

alcohol. 

oil. 

CaSO«    .. 

w 

w 

w 

w 

w 

w 

\v 

SnO,    .... 

w(s) 

ws 

ws 

s(w) 

sw 

sw 

sw 

A1(OH)3    .. 

w(s) 

ws 

ws 

s 

s(w?) 

sw 

s(  w) 

SnS    .... 

WS 

ws 

ws 

s(w) 

s(w) 

s 

ws 

BaSO4    .... 

ws 

WS 

ws 

s 

s 

S  (  W  ?  ) 

s  (  w  ?  ) 

ZnS    

w(s) 

ws 

ws 

s 

s(w?) 

s 

s(w?) 

ZnO  

ws 

ws 

s(w) 

s 

s 

s 

s 

CaC03   .... 

ws 

ws 

s 

s 

s 

s 

s 

Mg(OH)2    . 

s(w?) 

ws 

s 

s 

s 

s(w) 

sw 

Al 

sw 

s(w) 

s(w) 

s 

s 

S  (  W  ) 

s 

BaCO3  

ws 

ws 

ws 

s 

s 

sw 

s 

CuS   

ws 

s(w) 

s 

s 

s 

s 

s 

PbCr04   ... 

ws 

s(w?) 

s 

s 

s 

s 

s 

CU;O        (?)         . 

ws 

s 

s 

s 

s 

s 

s 

MoS2    

s(w?) 

s 

s 

s 

s 

s 

s 

PbS 

ws 

s 

s 

s 

s 

s 

s 

WS 

s 

s 

s 

s 

s 

s 

BaCrO4   .  .  . 

WS 

s 

s 

s 

s 

s 

s 

Pb304   

sw 

s 

s 

s 

s 

s 

s 

C    

sw 

s 

s 

s 

s 

s 

s 

Pbl 

s 

s 

OS 

s 

s 

OS 

s 

HgS   ..      .. 

s 

s 

s 

s 

s 

s 

s 

HgO  

s 

s 

s 

s 

s 

s 

0 

HgL    

s 

s 

s 

s 

s 

0 

OS 

Agl    

s 

s 

0 

s 

s 

0 

OS 

see  today.  I  have  done  some  work  along  these  lines  and  have  planned 
considerable  research  work  in  the  same  direction.  Meantime  these 
notes  might  as  well  be  available  to  others  in  suggesting  lines  of  useful 
research.  The  comments  to  be  made  on  the  above  tables  are  without 
end,  but  the  tables  are  given  here  mainly  to  suggest  the  possibilities 
of  further  work. 

The  question  arises  as  to  whether  it  might  not  be  possible  to  apply 
a  set  of  inequalities  such  as  those  of  Reinders,  or  even  to  apply 
Reinders'  inequalities  direct,  in  the  prediction  of  results  for  froth 
flotation.  In  froth  flotation  we  have  at  least  four  phases — solid,  water, 
oil,  and  gas — unless  the  oil  happens  to  be  soluble  in  water,  in  which 
case  we  are  reduced  to  a  solid,  a  solution,  and  a  gas.  We  have  inter- 
facial  tensions  between  each  two  of  the  phases,  making  six  tensions  al- 
together, and  mathematical  expressions  covering  such  a  case  must 
necessarily  be  much  more  complex  and  exhibit  a  greater  number  of 
possibilities.  The  problem  is  more  difficult,  but  it  should  be  capable  of 
solution.  Fig.  35  shows  a  fanciful  magnification  of  one  possible 
arrangement  of  the  particles  of  solid,  droplets  of  oil,  and  spherules 


WHY   DO   MINERALS   FLOAT? 


181 


of  air,  in  the  liquid  of  the  ore-pulp,  being  subjected  to  flotation,  at 
the  moment  when  a  bubble  begins  to  raise  a  particle  of  mineral  to  the 
surface. 

Fig.  36  shows  a  possible  way  of  applying  Reinders'  inequalities 
direct  without  any  modification.  It  is  assumed  that  the  oil  forms  an 
envelope  on  the  inner  surface  of  the  air  bubble  so  that  the  air  is 

Al  R 


-  WATER 


-  -  f     V  -  GAS  — 


FIG.'  35. 

nowhere  in  contact  with  water.  Mr.  Rickard7  has  called  our  attention 
to  the  work  of  Devaux,  published  in  the  annual  report  of  the  Smith- 
sonian Institute,  in  which  it  was  found  that  a  droplet  of  an  oil  when 
placed  upon  a  plane  surface  of  water  will  spread,  of  its  own  weight, 


A  I  R 


AIR 


WATER 


BUBBLE.     _ 


MINERAL 


FIG.   36. 


FIG.   37. 


until  it  forms  a  film  only  one  or  two  molecules  thick.  This  fact  allows 
an  explanation  of  how  the  small  amount  of  oil  used  in  the  froth- 
flotation  processes  could  be  so  efficient.  If  it  so  happens  that  the  oil 


'M.  d  8.  P.,  Sept.  11,  1915,  page  167. 


182  THE   FLOTATION   PROCESS 

could  coat  the  inner  surface  of  an  air  bubble,  the  powdered  mineral 
would  be  able  to  take  up  a  position  on  the  inter-face  between  the  water 
and  the  oil  without  any  reference  to  the  air  in  the  bubble. 

By  reason  of  the  known  low  adhesiveness  of  oil  and  water  it  is 
doubtful  if  the  air  bubbles  could  be  completely  mantled  by  oil,  as  the 
oil  would  be  too  liable  of  its  own  weight  to  slide  down  to  the  bottom 
of  the  bubble  to  the  position  indicated  in  Fig.  37.  Even  here,  the  oil 
could  carry  mineral  on  its  water  inter-face  (in  case  the  oil  and  water 
do  actually  get  into  contact)  and  Reinders'  criteria  would  still  apply. 
In  a  Callow  flotation  machine  having  glass  sides  it  is  sometimes  pos- 
sible to  see  particles  in  just  such  a  position.  However,  this  case  does 
not  prove  that  the  top  side  of  the  bubble  is  coated  with  oil  or  mineral, 
while  the  bubbles  of  a  mineral  froth  on  top  of  the  pulp  are  seen  to  be 
covered  completely  with  particles  of  mineral. 

If  the  mineral  tends  to  enter  the  oil  phase  completely  and  leave 
the  water,  the  mineral  grains  present  only  an  oil  surface  and  in  case 
oil  droplets  tend  to  collect  at  the  inter-face  between  water  and  air 
(by  Reinders '  criteria)  we  could  have  the  case  illustrated  in  Fig.  38. 

AfR 


FIG.  38. 

This  case,  as  well  as  the  one  illustrated  in  Fig.  36,  would  allow  of  the 
air  bubbles  becoming  completely  covered  with  oiled  mineral. 

Other  phases  are  possible,  but  these  are  given  to  show  how  very 
feasible  it  is  to  get  an  explanation  of  flotation  in  terms  of  inter-facial 
tensions. 

In  an  investigation  conducted  by  the  Minerals  Separation,  the 
1  contact  angle*  of  various  minerals  with  water  was  examined  to  find 
at  what  angle  the  mineral  had  to  come  in  contact  with  a  water  surface 
before  it  was  wetted  and  could  sink.8  A  glance  at  Clerk  Maxwell's 


8H.  L.  Sulman,  Trans.  Inst.  M.  &  M.,  1912. 


WHY   E>0   MINERALS    FLOAT?  183 

famous  paper  on  'Capillarity,'  upon  which  Reinders'  work  is  based, 
will  suggest  immediately  the  explanation  of  a  contact  angle,  and 
that  it  is  the  result  of  a  certain  equilibrium  of  inter-facial  tensions  of 
air,  water,  and  solid.  Valentiner9  has  likewise  investigated  the 
contact  angle  and  its  hysteresis  under  certain  conditions  and  has  con- 
nected it  very  definitely  with  capillary  phenomena.  There  can  be  no 
doubt  that  there  is  a  close  parallelism  between  the  angle  of  hysteresis 
of  the  contact  angle  and  the  ability  of  a  mineral  to  float.  But  if 
we  go  no  further  than  to  observe  the  parallelism  we  cannot  designate 
the  statement  of  the  parallelism  as  a  theory,  although  we  might  be 
able  to  predict  by  its  means  whether  a  mineral  would  float. 

To  go  into  this  a  little  farther,  and  indeed  along  the  line  suggested 
by  Mr.  Durell,  we  ought  to  consider  the  properties  of  the  surface 
layers  of  the  substances  involved.  For  example,  the  plane  surface  of 
water  in  contact  with  air  is  known  to  have  considerably  different 
properties  from  the  inner  bulk  of  the  water.  In  Fig.  39  the  film  is 

AIR 


BULK    \N/\TE.R 


FIG.  39. 

shown  magnified  in  thickness.  It  acts  like  a  tightly  stretched  elastic 
skin,  due  to  what  we  have  long  called  a  'surface  tension'  of  81  dynes 
per  centimetre,  as  is  usually  given  in  text-books.  (This  means  that 
for  a  strip  of  the  surface  film  one  centimetre  wide,  a  longitudinal 
tension  of  81  dynes  has  been  measured  at  ordinary  temperatures, 
and  there  is  a  definite  tension  for  each  temperature.)  This  tension 
of  the  surface  film  is  one  of  its  most  commonly  known  properties,  but 
some  other  interesting  points  about  it  are  given  in  the  following : 

Its  thickness,  varying  with  temperature  and  other  conditions,  has 
been  estimated10  to  be  all  the  way  from  4  X  10  5  to  10  8  cm.  Its  density 
averages  2.14  as  compared  with  1  for  bulk  water,  although  it  is  doubt- 
less more  dense  at  the  immediate  surface  next  to  the  air  and  gradually 


»'A  Theory  of  Flotation,'  Metall  und  Erz,  11:455,  1914. 
^Philosophical  Magazine,  20:502,  1910. 


184  THE  FLOTATION  PROCESS 

shades  off  into  that  of  bulk  water.  This  consideration  probably  ex- 
plains the  wide  variation  in  the  results  of  the  measurement  of  the 
thickness,  as  one  method  might  be  less  delicate  than  another  and 
hence  not  take  account  of  some  of  the  layers  of  the  film  that  are 
nearly  bulk  water  in  their  properties.  This  average  density,  how- 
ever, is  illustrative  of  the  magnitude  of  the  force  involved  because 
water  is  a  substance  that  resists  compression,  and  it  has  been  cal- 
culated from  the  known  compressibility  of  water  that  the  force 
necessary  to  compress  it  to  twice  its  ordinary  density  is  some  thousands 
of  atmospheres.  Such  a  compression  should  liberate  heat,  and,  in  fact, 
the  heat  liberated  when  a  definite  area  of  new  surface  film  is  formed 
has  been  measured  and  found11  to  be  0.00315  cal.  per  sq.  cm.  Being  so 
highly  compressed,  its  specific  heat  might  be  expected  to  be  different 
from  that  of  bulk  water  and  has  been  measured  as  being  nearly  0.45 
instead  of  1.  This  low  specific  heat  approximates  that  of  ice. 

One  important  property  of  this  film  is  that  it  will  often  take  up 
dissolved  substances  in  different  proportion  from  the  amounts  in  which 
they  are  taken  up  in  the  bulk  solution,  and  there  is  always  a  definite 
equilibrium  between  the  two.  This  is  known  as  surface  concentration 
or  'surface  adsorption/  and  has  been  dealt  with  mostly  in  colloid 
chemistry,  where  the  large  amount  of  surface  of  the  finely  divided 
solids  is  large  in  comparison  with  their  weight.  In  case  a  greater 
proportion  of  the  substance  is  concentrated  into  the  film  than  there 
is  into  the  bulk  water  we  have  positive  adsorption ;  and  in  the  reverse 
case,  negative  adsorption.  The  properties  of  these  inter-facial  films 
have  been  found  to  be  greatly  modified  by  small  amounts  of  dissolved 
substances  and  the  properties  of  colloids  are  hence  likewise  greatly 
changed  The  importance  of  the  study  of  inter-facial  films  becomes 
obvious. 

Finally,  there  is  a  most  important  fact  about  the  film  of  water  in 
contact  with  air.  It  has  been  found  that  there  is  a  difference  of 
potential  of  0.055  volts  between  the  two  surfaces  of  the  film.12  The 
density  of  the  static  electric  charge  at  this  potential  is  4  X  10 5 
coulombs  per  sq.  cm.  This  electric  charge  is  markedly  influenced  by 
electrolytes  in  solution  and  can  be  increased  or  decreased,  even  pass- 
ing through  zero  and  then  increasing  in  the  opposite  sign.  All  inter- 
facial  films  have  likewise  been  found  to  be  charged  in  one  way  or 
other.  Industrial  applications  of  this  fact  are  legion.  All  the  tech- 
nical handling  of  clays  is  now  conditioned  by  the  use  of  electrolytes  in 


,  20:502,  1910. 
.,  27:297,  1914,  and  28:367,  1914. 


WHY    DO    MINERALS    FLOAT?  185 

this  manner,  and  the  question  of  emulsions  of  all  kinds  of  oils  in 
water  is  closely  bound  up  with  it.  Cottrell's  precipitation  process  of 
suspended  particles  of  solids  or  liquids  in  gases  does  not  escape  these 
considerations.  Small  particles  of  solids,  liquids,  or  gases  suspended 
in  either  liquid  or  gaseous  media  are  found  commonly  to  carry  electric 
charges,  due  to  various  combinations  of  factors  which  affect  the  double 
electric  layer  of  the  inter-facial  films. 

Since  the  size  of  many  of  the  particles  of  minerals  treated  by 
flotation  is  of  the  same  magnitude  as  that  of  many  colloids  we  cannot 
escape  from  calling  ore-slime  "coarse  suspension  colloids,"  and  must 
apply  all  the  laws  of  colloid  chemistry  to  our  problem. 

The  electric  charges  on  suspended  particles  allow  another  possible 
explanation  of  flotation  phenomena.  We  find  in  some  of  the  colloid 
chemical  literature13  that  quartz  particles  when  suspended  in  water 
are  negatively  charged,  pyrite  particles  positively  charged,14  oil  drop- 
lets are  negatively  charged,  and  air  bubbles  negatively  charged.15 
The  charges  are  somewhat  small  compared  with  the  weight  of  the 
particles,  so  that  they  are  hardly  strong  enough  to  cause  negatively- 
charged  quartz  to  stick  to  positively-charged  pyrite,  as  they  can  have 
only  a  few  points  of  contact,  and  currents  in  the  water  could  easily 
tear  them  apart.  However,  the  negatively-charged  droplet  of  oil, 
which  is  repelled  from  a  negatively-charged  particle  of  quartz,  can 
wrap  itself  around  the  positively-charged  pyrite  particle  so  that  they 
will  stick  together,  and  the  same  applies  to  air  bubbles.  The  other 
sulphides  known  to  be  flotative  have  positive  charges  when  suspended 
in  water  or  can  be  made  to  assume  positive  charges  by  the  use  of  the 
proper  amount  of  the  proper  electrolyte.  So  it  can  be  seen  that  the 
application  of  these  principles  gives  no  difficulty  in  explaining  flota- 
tion from  an  entirely  new  standpoint.!  The  large  effect  of  a  small 
amount  of  sulphuric  acid  on  the  conditions  of  flotation  does  not  seem 
strange  at  all  in  this  light,  and  we  do  not  have  to  retreat  to  the  purely 


izKolloid  Chemische  Beihefte,  2 : 84. 

^Zeitschrift  fur  physiJcaliscUe  Chemie,  89:91,  1914. 

isSee  foot-note  No.  10. 

tit  would  appear  that  at  the  instigation  of  J.  M.  Callow,  the  Mellon 
Institute  of  Pittsburg,  under  the  direction  of  R.  C.  Bacon,  also  formulated  this 
same  theory,  and  for  a  long  time  has  done  research  work  in  this  direction, 
this  work  and  continuation  of  it  at  the  Bureau  of  Mines  at  Salt  Lake  City 
seem  to  support  the  logic  of  this  theory.  A  paper  on  the  same  subject  was 
read  by  Mr.  Callow  at  the  October  meeting  of  the  American  Institute  of 
Mining  Engineers  in  Salt  Lake  City.  See  page  231  of  this  book. 


186  THE  FLOTATION  PROCESS 

imaginary  supposition  that  osmotic  pressure  is  acting  through  the 
surface  of  the  mineral,  as  does  Mr.  Durell. 

The  inter-facial  tension  and  the  charge  on  the  inter-facial  film  are 
two  different  physical  properties  of  one  and  the  same  thing.  I  have 
shown  that  an  appeal  to  either  property  is  enough  to  build  up  a  work- 
ing picture  of  flotation  phenomena  that  is  simpler  and  more  probable 
than  that  of  Mr.  Durell.  I  do  not  know  how  much  there  is  in  his  con- 
tention that  air  bubbles  "will  not  attach  themselves  directly  to  the 
particles,  or  that  only  the  dissolved  air  can  thus  attach  itself ;  it  may 
be  that  this  is  all  correct,  without  interfering  with  the  explanation 
that  I  have  put  forward.  However,  I  hesitate  to  accept  such  a  con- 
ception. The  underlying  cause  of  the  tensions  and  of  the  electric 
charges  is  the  same  thing — some  strange  molecular,  atomic,  or  other 
force  manifested  in  'adhesion/  'cohesion,'  or  even  'gravitation/  if 
you  please.  No  one  can  claim  that  electric  charges  carry  the  whole 
explanation  of  flotation,  nor  can  it  be  stated  that  it  is  merely  a  ques- 
tion of  a  balancing  of  inter-facial  tensions.  Both  will  doubtless  have  to 
be  considered. 

Although  much  more  could  be  said  on  the  subject,  I  have  only 
attempted  to  point  out  that  there  are  certain  scientific  principles  that 
can  be  applied  to  our  problem,  with  great  chances  of  success,  in  bring- 
ing us  nearer  to  a  definite  understanding  of  flotation.  Physical  chem- 
istry has  been  a  recognized  tool  of  metallurgists  for  some  time,  al- 
though little  used  by  most  of  them,  and  now  a  particular  branch  of 
physical  chemistry — colloid  chemistry — is  beckoning  to  us  alluringly. 
All  questions  of  the  treatment  of  ore-slime  should  be  studied  in  this 
new  light.  The  results  of  an  application  of  this  idea  in  our  own 
laboratory  have  been  astonishing,  and  we  hope  that  we  may  soon  be 
able  to  publish  them. 


WHY    IS    FLOTATION?  187 

WHY  IS   FLOTATION? 

(From  the  Mining  and  Scientific  Press  of  October  30,  1915) 
The  Editor: 

Sir — Mr.  Durell's  article  on  this  subject  in  your  issue  of  Septem- 
ber 18  is  interesting.  I  believe  that  an  exchange  of  ideas  on  this 
subject  is  very  desirable,  and  it  may  be  that  some  of  the  information 
that  I  have  collected  may  be  of  interest  to  the  readers  of  the  Press. 

The  arguments  which  Mr.  Durell's  article  presents  are,  briefly, 
that  floatable  particles  cannot  attach  themselves  to  previously  formed 
bubbles,  but  must  be  floated  by  bubbles  which  form  themselves  on 
the  surface  of  the  particles  so  that  there  is  no  surface  film  of  water 
between  the  particle  and  the  air.  To  explain  the  formation  of  these, 
Mr.  Durell  assumes  that  the  water  is  super-saturated  with  dissolved 
air  and  that  there  is  a  certain  amount  of  "occluded"  air  on  and 
in  the  surface  of  the  particle,  and  that  these  combine  to  form  bubbles. 
That  this  occluded  air  may  be  present  is  certainly  possible,  but 
that  it  would  be  liberated  with  sufficient  rapidity  to  float  the  particles 
does  not  seem  probable.  That  the  water  in  a  M.  S.  type  of  machine 
is  supersaturated  with  air  is  also  probable,  but  I  cannot  see  how 
the  water  in  a  Callow  or  other  pneumatic  machine  can  become 
greatly  super-saturated  by  the  introduction  of  air  through  a  coarsely 
porous  medium  such  as  canvas  twill. 

The  idea  of  super-saturating  the  water  with  air  is  not  new.  As 
early  as  1907  D.  H.  Norris  patented  this  process.  (U.  S.  patents 
No.  864,856  and  873,586.)  Mr.  Norris  saturated  water  with  air  at  a 
pressure  of  several  atmospheres,  and  introduced  it  into  an  open  tank 
at  normal  pressure,  where  the  excess  air  formed  what  he  called 
"infinitely  small  nascent  bubbles  of  gas"  which  were  supposed  to 
float  the  sulphide  particles.  So  far  as  I  know,  this  idea  has  never 
been  put  into  successful  operation. 

As  to  Mr.  Durell's  statement  that  the  dissolved  and  occluded  air 
are  indispensable;  if  it  is  true,  previous  boiling  of  the  pulp,  which 
would  drive  out  all  of  the  dissolved  and  some  of  the  occluded  air, 
should  interfere  considerably  with  flotation,  especially  in  a  pneumatic 
machine.  I  have  seen  this  done  in  the  laboratory  of  the  General 
Engineering  Company.  The  subsequent  flotation  took  place  with 
practically  the  same  rapidity  and  cleanliness  as  when  the  same  ore 
was  floated  without  boiling  of  the  pulp.  Furthermore  it  has  been 
my  observation,  that  when  a  carbonate  ore  is  treated  with  soluble 


188  THE   FLOTATION    PROCESS 

sulphides  for  the  purpose  of  forming  an  artificial  film  of  sulphide 
on  the  surface  of  the  mineral  particles,  much  better  results  are 
obtained  when  a  small  amount  of  alkali  is  added  to  the  pulp  to 
remove  any  traces  of  H2S  gas.  This  can  also  be  accomplished  by 
the  use  of  S02,  which  reacts  with  the  H2S  to  form  sulphur  and 
H20,  and  does  not  leave  an  alkaline  pulp.  Were  Mr.  Durell's 
hypothesis  true,  this  gas  should  be  beneficial  rather  than  detrimental, 
and  it  would  seem  that  the  general  effect  of  artificial  sulphiding 
would  be  to  reduce  the  amount  of  occluded  air  rather  than  increase 
it,  as  some  of  it  would  undoubtedly  be  displaced  by  H2S  which  would 
later  be  removed. 

I  cannot  agree  with  Mr.  Durell's  statement  that  floatable  particles 
will  not  attach  themselves  to  previously  formed  air  bubbles.  I  under- 
stand that  in  the  suit  of  the  Minerals  Separation,  Ltd.,  v.  Miami 
Copper  Co.,  heard  at  Wilmington  May  1915,  the  plaintiff  presented 
to  the  Court  a  moving  picture  of  an  experiment  in  which  it  was 
shown  under  just  what  conditions  the  particle  would  attach  itself  to 
the  bubble.  Aside  from  that,  it  is  not  a  far-fetched  assumption  that 
the  air  bubbles  in  an  oil-emulsion  have  mantles  of  oil.  Their  property 
of  frothing  would  so  indicate,  and,  in  that  case,  the  surface  films 
of  water  surrounding  them  would  not  differ  materially  from  the  films 
surrounding  drops  of  oil  suspended  in  water.  That  such  drops  of 
oil  can  collect  floatable  particles  out  of  an  ore  can  easily  be  proved 
by  shaking  oil  with  a  mixture  of  galena  and  sand  suspended  in  water. 
When  the  oil  has  collected,  the  drops  will  be  seen  to  be  covered 
with  the  galena.  If  we  imagine  the  centres  of  these  drops  to  be  filled 
with  air  instead  of  oil,  we  have  conditions  which  might  easily  hold 
in  an  actual  flotation  machine. 

On  the  whole,  Mr.  Durell's  hypothesis  does  not  seem  to  conform 
with  actual  flotation  practice.  There  are  other  theories  that  explain 
flotation  in  better  conformity  with  known  scientific  facts.  T.  J. 
Hoover,  for  instance,  in  his  book  'Concentrating  Ores  by  Flotation,' 
presents  a  consistent  theory,  and  J.  M.  Callow  presented  a  paper 
to  the  Utah  Section  of  the  American  Institute  of  Mining  Engineers 
in  which  were  set  out  some  theories  based  on  experimental  work 
done  at  the  Mellon  Institute  and  at  the  local  station  of  the  U.  S. 
Bureau  of  Mines.  This  paper*  will  undoubtedly  be  published  soon 
in  the  transactions  of  the  Institute. 

JAMES  A.  BLOCK. 

Salt  Lake  City,  October  6. 


*See  page  231  of  this  book. 


AIR-FROTH    FLOTATION II  189 

AIR-FROTH   FLOTATION— II 

(From  the  Mining  and  Scientific  Press  of  November  6,  1915) 

[In  our  issue  of  October  16  we  gave  an  excerpt  from  the  speech 
made  by  Mr.  W.  A.  Scott,  counsel  for  defendant  in  the  case  of  Minerals 
Separation,  Limited,  v.  Miami  Copper  Company.  We  follow  this  now 
with  lengthy  quotations  from  the  speeches  of  Messrs.  Henry  D.  Wil- 
liams and  W.  Houston  Kenyon,  of  counsel  for  the  complainant.  In 
the  first  excerpt  Mr.  Williams  discusses  the  article  by  the  three 
students  at  the  University  of  California,  as  published  in  the  college 
magazine,  The  California  Journal  of  Technology.  The  major  portion 
of  that  article  appeared  in  our  issue  of  July  31,  1915,  to  which  the 
reader  is  referred*  in  order  to  follow  the  lawyer's  remarks.  In  the 
second  and  third  excerpts  Mr.  Kenyon  discusses  some  of  the  physics 
of  the  flotation  process.  Of  course,  the  reader  must  remember  that 
this  exposition  of  the  subject,  like  that  of  Mr.  Scott,  is  not  to  be  taken 
as  a  scientific  thesis ;  it  is  essentially  an  ex  parte  explanation,  but  even 
as  such  it  is  extremely  interesting  to  metallurgists.  The  first  patent 
in  suit,  to  which  reference  is  made,  is  No.  835,120. — EDITOR.] 

MR.  WILLIAMS  :  The  California  Journal  of  Technology  is  evidence 
of  the  interest  that  the  metallurgical  world  took  in  the  Elmore  process. 
The  title  is  'Experiments  on  the  Elmore  Process  of  Oil  Concentration.' 
The  conclusion  is : 

"The  work  above  outlined  suggests  many  lines  of  further  investi- 
gation, and  as  these  come  to  be  worked  out,  the  process  will  become 
more  valuable  and  of  more  general  application." 

What  process?    The  Elmore  process. 

In  1903,  the  Elmore  process  was  a  hope  of  the  metallurgical  world. 

Incidentally,  the  students  discovered  something  else,  and,  for  the 
first  time,  gave  to  the  world  the  foam  effect.  Full  disclosure  as  to  a 
mode  of  operation  which  would  produce  an  oil  foam,  they,  for  the  first 
time  in  the  history  of  metallurgy,  gave  to  the  world. 

That  was  an  incident  of  their  careful  investigation,  but  the  article 
itself  is  on  the  Elmore  process,  and  it  says  that  the  Elmore  process  was 
then  a  hope  of  the  metallurgical  world. 

THE  COURT  :  Mr.  Williams,  if  there  was  a  disclosure  of  the  process, 
although  a  misnomer,  what  would  be  the  effect  of  that  disclosure  ? 

MR.  WILLIAMS  :    The  name,  obviously,  has  nothing  to  do  with  it. 

THE  COURT  :    No. 


*See  page  102  of  this  book. 


190  THE   FLOTATION    PROCESS 

MB.  WILLIAMS  :  I  was  particularly  directing  my  attention  to  the 
fact  that  Mr.  Sheridan  took  those  last  three  lines  as  something  which 
was  directed  solely  and  wholly  to  that  small  part  of  this  article  which 
deals  with  the  foam  effect. 

THE  COURT  :    Oh,  I  understand. 

MR.  WILLIAMS  :  And  I  was  merely  pointing  to  the  fact  that  those 
lines  must  have  referred  to  this  Elmore  process  as  a  hope  of  the 
metallurgical  world. 

The  foam  effect  here  disclosed,  which  is  recommended  as  employ- 
ing 8.9%  of  oil — it  being  clearly  shown  that  nothing  else  is  worth 
anything — 8.9%  of  oil  and  salt  solution,  an  ore  containing  light  flaky 
minerals,  such  as  molybdenite;  and  another  one  of  the  same  kind  is 
graphite,  and  I  do  not  know  any  others — certainly  not  copper,  cer- 
tainly not  zinc.  Galena  and  blende  are  not  flaky.  Galena  is  almost 
cubical  in  its  fracture.  They  call  attention  to  the  study  of  the  frac- 
ture of  minerals.  They  worked  out  this  foam  effect,  which  they  give 
to  the  world,  with  the  recommendation  that  8.9%  of  oil  be  used,  as 
something  which  may  possibly  be  useful  with  light  flaky  minerals, 
and  that  became  a  part  of  the  constructive  knowledge  of  the  world 
in  November  1903. 

It  is  remarkable  that  it  was  buried  and  lost,  and  that  it  took  three 
years  of  litigation  to  unearth  it.  That  is  quite  remarkable,  especially 
that  it  should  have  been  buried  and  lost  in  the  University  of  Cali- 
fornia, which  is  in  the  heart  or  the  centre  of  the  important  mining 
interests  on  the  Pacific  Coast,  and  in  the  Great  West. 

But  that  is  all  there  is  there,  and  the  most  significant  thing  about 
it  is  that  it  tells  the  investigator:  We  have  tried  2.1%,  and  the  result 
is  hopeless.  We  have  tried  5.3%,  and  the  result  is  almost  as  bad.  But 
we  have  tried  8.9%,  and  there  is  some  hope  in  that.  Now,  proceed; 
investigate. 

But  very  evidently,  nobody  proceeded  and  investigated.  There  is 
not  any  practical  art,  unless  it  be  Elmore.  There  was  not  any  mill 
that  made  any  use  of  any  of  these  patents  that  have  been  referred  to. 
Haynes  lightly  touched  upon;  Everson,  the  foundation  of  the  de- 
fendant's case — why  these  very  students  in  this  article  tell  the  exact 
truth  about  Everson.  I  am  sorry  they  did  not  write  more,  because 
they  would  have  been  impartial,  and  they  would  have  possibly  given 
us  a  fair,  unbiased  interpretation  of  the  patent. 

"In  1886  Carrie  J.  Everson  of  Chicago*  contributed  the  idea  that 


*In  her  first  patent,  No.  349,157,  she  is  described  as  "of  Chicago,  Illinois," 
but  in  No.  471,174  she  is  said  to  be  "of  Denver,  Colorado." — EDITOR. 


AIR-FROTH    FLOTATION II  191 

the  concentration  was  aided  by  the  presence  of  an  acid  solution,  and 
patented  the  same." 

That  is  just  exactly  what  Carrie  Everson  did  contribute.  It  is  an 
exact  statement,  and  that  is  preceded  by  reference  to  another  patent, 
which  the  defendant  has  not  seen  fit  to  refer  to,  although  it  has  figured 
in  some  other  litigation — the  patent  of  Tunbridge,  erroneously  here 
spelled  '  Turnbridge. '  That  is  set  forth  here  as  the  first  patent  for 
utilizing  oil,  and  its  date  is  given  as  1878.  But  it  is  of  slight  rele- 
vancy, and  the  defendant  has  not  relied  upon  it,  and  it  is,  as  your 
Honor  will  note,  later  than  Haynes. 

As  a  matter  of  fact,  the  reference  to  this  patent  would  indicate  a 
study  of  the  Everson  patent,  because  the  Everson  patent  disclaims 
the  Tunbridge  patent.  It  does  so  with  quite  some  labor.  It  is  the 
thing  that  Carrie  Everson  had  to  distinguish  from;  that  I  think  ac- 
counts for  the  reference  to  that  patent. 

These  students  probably  investigated  the  patent  situation,  and  so 
they  referred  to  the  Tunbridge  patent  and  the  Everson  patent,  and 
they  tell  the  exact  truth  of  the  contribution  of  Carrie  J.  Everson  to 
the  art  of  the  idea  that  the  concentration  was  aided  by  the  presence 
of  an  acid  solution. 

Then  these  young  men  say,  and  they  say  truthfully : 

1 '  But  the  absence  of  a  successful  method  of  separating  the  mineral 
from  the  oil  prevented  the  practical  application  of  these  prior 
patents." 

"Well,  they  do  not  tell  the  whole  truth  about  that,  but  that  is  un- 
doubtedly one  of  the  reasons,  and  the  important  thing  is  that  these 
prior  patents,  Tunbridge  and  Everson,  were  not  practically  applied. 
That  they  were  not  capable  of  practicable  application  would  be  the 
reasonable  presumption,  but  that  is  the  fact.  And  then  these  students 
go  into  the  subject  of  the  removal  of  the  oil.  Of  course,  with  17.1% 
of  oil,  which  is  342  pounds  of  oil  to  the  ton  of  ore,  and  if  out  of  the 
ton  of  ore  you  got  700  Ib.  of  concentrate,  that  would  be  a  fair  average. 
"With  these  342  Ib.  of  oil,  you  see  the  oil  would  be  about  50%  of  the 
concentrate.  You  would  have  a  great  mass  of  oil  with  the  concen- 
trate, and  unless  you  could  successfully  get  rid  of  that  oil,  it  would  be 
troublesome;  and,  again,  the  cost  of  that  oil  was  such  that  it  must 
be  possible  to  recover  and  use  it  over  again.  It  has  acted  merely  in  a 
physical  manner.  It  has  not  changed  its  constitution  at  all.  So,  if 
you  could  bring  it  out,  separate  it,  and  send  it  through  again,  there 
was  some  hope ;  it  was  Elmore  who  did  that. 

The  students  say  that  burning  of  the  oil  was  tried,  which  left  a 


192  THE  FLOTATION  PROCESS 

difficult  residue  to  treat,  and  the  large  consumption  of  the  oil  made  the 
method  too  expensive.  That  is  undoubtedly  true. 

"It  was  not  until  July  1900  that  this  difficulty  was  overcome  by 
means  of  a  special  machine,  similar  in  most  respects  to  that  which  is 
used  in  sugar  factories  and  in  milk  and  cream  separation.  This  con- 
tribution by  Mr.  Elmore  then  made  the  process  feasible. ' ' 

Now,  we  will  note  here  that  they  mean  the  process  of  oil  concen- 
tration. These  young  men  were  looking  at  it  solely  from  the  view- 
point of  something  which  utilized  oil  in  the  concentration  of  ores — 
they  were  not  concerned  particularly  with  methods,  but  they  were 
looking  at  it  always  from  that  viewpoint;  that  is  why  they  refer  to 
Tunbridge,  and  why  they  refer  to  Everson,  but  there  is  not  a  thought 
or  suggestion  running  through  here  that  the  Everson  patent,  which 
they  say  has  proved  of  no  practical  value,  makes  any  suggestion  of 
flotation.  Everson  merely  contributed  the  use  of  acid. 


MR.  WILLIAMS  :  Prior  to  the  invention  of  the  first  patent  in  suit, 
and  looking  only  to  what  men  did,  we  find  that  wet-concentration 
processes  were  the  solution  of  the  ore-concentration  problem.  They 
were  the  processes  that  have  been  described  here,  and  that  I  need  not 
describe  again ;  processes  that  depend  upon  gravity  and  shaking  and 
motion  of  finely  ground  ore  suspended  in  moving  water,  the  separation 
depending  upon  the  difference  in  sinking-power  of  the  metal  and  the 
gangue ;  wet-concentration  processes  that  are  in  use  to  a  tremendous 
extent  still,  but  that  are  being  superseded  in  the  last  two  or  three 
years  to  an  astonishing  degree  by  the  processes  of  the  patents  in  suit. 

No,  in  these  wet-concentration  processes  advantage  was  taken  of 
the  fact  that  the  metal  had  a  higher  specific  gravity  in  the  average 
than  the  gangue,  and  the  laws  of  nature  were  followed.  The  heavier 
thing  was  allowed  to  settle,  and  circumstances  and  conditions  were  so 
controlled  that  it  would  have  a  chance  to  settle  away  while  the  gangue 
would  be  left  suspended.  The  gangue  would  be  floated  in  mid-bulk 
of  the  liquid,  and  up  and  down  and  all  around,  and  finally  floated  off 
over  a  dam. 

But  all  wet-concentration  processes — and  the  machinery  for  car- 
rying them  out  has  exercised  the  ingenuity  of  inventors  for  thirty 
years — all  wet-concentration  processes  were  useless  on  slime,  and  the 
fact  that  the  concentration  was  by  such  processes  raised  a  hard  and 
fast  limitation  to  the  extent  that  you  could  grind  ore.  The  grinding 
must  be  coarse.  The  grinding  must  be  so  done  as  to  produce  the  mini- 
mum of  metal-dust;  and  so  grinding  machines  were  invented  to  that 


AIR-FROTH    FLOTATION II  193 

end,  to  prevent  the  production  of  the  fine  dust-like  particles  of  metal 
in  the  general  grinding  of  the  ore.  All  wet-concentration  processes 
are  useless  on  slimes.  They  will  not  settle.  They  will  not  obey  the 
laws  of  gravity.  They  will  stay  up  with  the  gangue.  They  will  float 
off  with  the  gangue.  They  will  run  to  waste.  And  hence  we  have 
these  tailings  in  Australia  and  here,  of  millions  of  tons,  where  the 
slimed  metal,  the  finest  of  the  metal,  has  all  run  off,  because  it  could 
not  be  recovered.  With  such  concentration  processes  the  best  that 
could  be  done  was  from  60  to  70%  recovery.  Prof.  Fulton  gave  70% 
as  the  outside  limit — 60  or  70%  of  the  sulphide  metal  in  the  original 
ore.  And  yet  men  persisted  in  using  that  process. 

Elmore,  about  the  opening  of  this  century,  about  1900 — his  pat- 
ents were  a  year  or  two  earlier — pame  in  with  his  process  to  reverse 
the  laws  of  nature.  Instead  of  finding  the  heavier  thing  at  the  bot- 
tom, Elmore  said:  "I  will  carry  it  to  the  top." 

Again  a  process  useless  on  slime.  Again  a  process  requiring  coarse 
grinding  as  before.  The  concentrate  at  the  top  now  instead  of  at  the 
bottom.  The  theory  of  operation  was  an  oil  lake.  I  like  that  word 
'lake.'  It  is  used  by  the  California  Journal  students — an  oil  lake. 
Air  entrainment  was  fatal.  Ingenuity  was  exercised  to  so  mix  the 
oil  lake  and  the  ore  as  not  to  entrap  air.  Oil  emulsion  was  fatal. 
The  amount  of  oil  we  know  was  100  to  300%  on  the  ore.  And  yet 
men  did  that  thing.  Men  paid  that  price,  and  the  loss  on  every  100 
Ib.  of  oil  was  9  or  10  Ib.  at  each  cycle.  The  other  90  Ib.  had  to  be 
taken  out,  and  preserved,  and  used  over  again. 

And  Cattermole.  The  very  men  who  afterward  made  the  invention 
of  the  first  patent  in  suit  spent  two  years  and  a  half  developing  that 
Cattermole  process,  a  really  beautiful  idea,  the  first  process  addressed 
to  the  slime  problem.  Said  Cattermole  to  himself: 

"Now,  if  I  can  have  fine  grinding  of  the  gangue  and  coarse 
grinding  of  the  metal,  I  can  separate  the  metal  out  by  its  dropping 
and  by  the  gangue  floating. ' '  For  right  there  is  an  interesting  prin- 
ciple of  physics.  "When  a  particle  is  floating  in  water,  its  tendency  to 
sink  is  determined  partly  by  its  weight.  The  weight  tends  to  carry  it 
down  if  it  is  heavier  than  water.  The  surface  of  the  particle  tends 
to  resist  that,  tends  to  keep  it  up.  If  the  surface  is  greater,  in  respect 
to  the  weight,  it  will  not  go  down  so  fast.  If  the  weight  is  greater  in 
respect  to  the  surface,  it  will  go  down  faster.  Now,  if  you  imagine  a 
little  cube  of  metal  suspended  in  water,  and  imagine  its  linear  dimen- 
sions doubled  in  all  directions,  the  surface  will  have  been  squared, 
and  that  is  the  thing  which  resists  dropping,  while  the  weight  will 


194  THE  FLOTATION  PROCESS 

have  been  cubed.  The  weight  has  increased  faster  than  the  surface. 
Therefore  that  doubled  cube  will  sink  faster  through  water.  That 
law,  of  the  square  as  to  the  surface,  resisting  sinking,  and  the  cube  as 
to  the  weight  compelling  sinking,  is  the  thing  that  makes  big  particles 
drop  more  in  accordance  with  their  true  specific  gravity,  but  fine  par- 
ticles like  slimes  refuse  to  obey  the  laws  of  specific  gravity,  and  con- 
tinue to  float  and  not  sink,  whether  they  be  mineral  or  whether  they 
be  metal. 

As  Dr.  Liebmann  illustrated  on  the  stand,  if  the  rain  came  down 
in  a  shaft  it  would  kill  us  all.  When  the  same  amount  of  rain  is 
broken  into  small  drops,  it  does  not  kill  us.  Why  ?  Because  the  sur- 
face has  been  so  enormously  increased  with  respect  to  the  weight,  or 
vice  versa  the  weight  diminished  with  respect  to  the  surface.  So  the 
resisting  surface  makes  those  drops  come  down,  not  like  bullets,  but 
gently.  And  going  a  step  further,  when  the  particles  are  smaller 
still,  they  will  not  come  down  at  all.  They  will  float  like  the  summer 
cloud  in  the  sky.  Their  specific  gravity  is  just  as  great  as  it  ever 
was  with  respect  to  the  air,  but  they  are  so  small  that  they  are  floated. 

THE  COURT:  Is  it  because  they  are  so  small,  or  is  it  because  of 
their  form  ? 

MR.  KENYON  :  Their  form  would  have  a  tendency  to  be  spherical 
in  all  cases,  but  it  is  a  function  of  their  size. 

THE  COURT:     I  suppose  if  you  dropped  a  needle  into  water  and 
kept  it  point  downward,  it  would  go  down  fast. 

MR.  KENYON  :  Yes,  it  would  go  right  down.  Drop  it  sidewise,  so 
that  you  have  multiplied  the  surface  without  changing  the  weight,  and 
it  will  stay  right  there. 

Now.  Cattermole  conceived  this  brilliant  idea:  If  I  can  only  make 
my  gangue  particles  fine,  they  will  stay  up  there  indefinitely.  If  I 
can  only  make  my  metal  particles  big,  they  will  drop  faster.  He  knew 
he  could  not  do  that  in  grinding.  Let  the  inventor  of  the  future,  if 
he  be  here  present,  take  this  for  a  cue :  A  grinding  machine  that  at 
the  same  time  will  grind  the  gangue  fine  and  the  metal  coarse  will 
revolutionize  all  these  processes.  Cattermole  knew  that  could  not  be 
done  in  grinding,  so  he  said :  "I  will  grind  it  all  fine,  and  then  by  the 
gluing  effect  of  oil,  particle  to  particle,  oil  which  goes  to  metal  and 
does  not  go  to  gangue,  I  will  roll  and  work  my  metal  particles  into 
big  metal  particles,  whereas  the  gangue  will  remain  as  fine  as  it  was 
ground ;  and  then  when  I  have  done  that,  my  big  metal  particles,  my 
granules,  my  spherules,  will  drop  and  the  gangue  will  go  up. ' ' 

That  was  the  Cattermole  idea,  and  men  proposed  to  do  that  thing, 


AIR-FROTH    FLOTATION II 


195 


and  these  plaintiffs,  and  the  world  would  have  been  concentrating 
their  ore  by  that  process  today  in  preference  to  all  others,  probably, 
but  that  the  invention  of  the  first  patent  in  suit  was  made. 

The   Cattermole  idea  of  operation  was  by  oil  adhesiveness  and 


FlG.    40.      DRAWING    ACCOMPANYING    A.    E.    CATTERMOLE'S    PATENT,    NO.    777,273,    OF 

DECEMBER    13,    1904. 

mixing.  Air  entrainment  was  a  trouble.  Flotation  scum  was  a  loss. 
Two  to  five  per  cent  of  oil  on  the  ore  (4  to  10%  on  the  metal;  it  was 
a  rich  50%  metal  ore)  was  the  amount,  and  if  the  effects  were  dimin- 
ishing, then  they  increased  slightly  the  amount  of  oil.  (Higgins, 
Printed  Record,  p.  212.  Q.  43,  44.) 


196  THE   FLOTATION    PROCESS 

Thereupon  a  recess  was  taken  until  two  o'clock  p.m.  same  day. 

THE  COURT:  Mr.  Kenyon,  I  was  very  much  interested  in  the 
remark  you  were  making  before  recess  on  the  matter  of  the  difference 
between  big  particles  and  little  particles,  in  the  strength  of  their 
power  to  overcome  resistance.  Now,  entirely  aside  from  surface  ten- 
sion as  such,  and  I  mean  that  sort  of  tension  to  enable  very  minute 
particles,  although  having  a  greater  specific  gravity  than  other  par- 
ticles, to  float  on  the  surface.  Aside  from  that,  and  aside  from  the 
case  in  which  the  mineral  particles  having  greater  specific  gravity 
are  attached  to  any  medium  of  buoyant  character  which  tends  to  sup- 
port them,  these  small  particles,  if  once  placed  beneath  the  surface 
of  the  water,  having  greater  specific  gravity,  of  course,  would  sink. 

MR.  KENYON:  Yes,  and  No.  The  coarsest  will  sink  at  once.  The 
finest  of  them  would  ultimately  sink,  but  the  finest  of  them  would  take 
so  long  to  sink  that  it  is  impracticable  to  separate  them  or  do  anything 
with  them  by  sinking,  and  that  was  the  slimes  problem  in  all  these 
metallurgical  operations.  They  would  float  there.  They  would  float 
in  the  liquid.  When  you  get  down  to  a  certain  ultimate  point  of 
fineness,  whether  it  be  metal  or  gangue,  it  will  float  in  the  water  under- 
neath the  surface. 

THE  COURT  :    Underneath  the  surface  ? 

MR.  KENYON  :    Underneath  the  surface. 

THE  COURT  :    But  still  they  would  gradually  sink  ? 

MR.  KENYON  :    After  a  long,  long  time. 

THE  COURT:  I  would  like  to  understand  you.  Of  course,  we  all 
know  that  if  we  could  conceive  of  a  perfect  vacuum,  both  a  bullet 
and  a  feather  will  go  down  together. 

MR.  KENYON  :    Under  the  law  of  their  specific  gravity  absolutely. 

THE  COURT  :  When  you  come,  however,  to  a  resisting  medium  ( I 
do  not  care  whether  it  is  air  or  water)  then  you  have  a  different 
proposition,  and  there  you  have  a  resistance  which  has  to  be  over- 
come, and  as  you  proceed  arithmetically  the  resistance  increases  geo- 
metrically, I  believe.  Is  that  right  ? 

MR.  KENYON:    Yes. 

THE  COURT  :  My  question  is  whether  these  particles  would  finally 
sink.  I  want  to  get  the  theory  if  I  can.  Aside  from  the  surface 
tension,  if  you  once  get  those  particles  underneath  the  surface  of  the 
water,  not  attached  to  any  bubble  or  any  substance  which  has  a  less 
specific  gravity  than  water,  will  they  not  sink,  although  at  a  greatly 
diminished  rate  ? 

MR.  KENYON:     They  will  ultimately  sink,  although  there  may  be 


AIR-FROTH    FLOTATION II  197 

what  they  call  a  colloidal  condition,  which  has  been  somewhat  dis- 
cussed here — clays  are  very  colloidal,  and  have  a  tendency  to  keep 
them  in  suspension  perhaps  for  days  before  they  would  sink.  Even 
they  will,  as  I  understand  it,  ultimately  sink. 

THE  COURT  :    Ultimately  ? 

MR.  KEN  YON  :  The  least  little  jar  or  agitation  will  send  them  right 
up  again.  The  whole  slime  problem  and  difficulty  in  all  metallurgical 
operations,  and  in  the  cyaniding  processes  as  well  as  concentration 
processes,  turn  just  on  the  long  length  of  time  it  takes  the  fine 
particles  to  settle  to  the  bottom.  They  will  float  an  inch  below,  two 
inches  below,  three  inches  below,  all  around,  almost  indefinitely, 
making  muddy  water. 

THE  COURT  :  The  very  instant  this  material  passes  into  a  larger 
mesh  and  you  have  a  larger  particle,  it  will  overcome  that  resistance  ? 

MR.  KENYON  :  Yes,  sir,  and  then  the  weight  increases  by  the  cube, 
whereas  the  resistance  only  increases  by  the  square. 

THE  COURT  :    I  see. 

MR.  KENYON:  That  is  the  mathematical  theory  of  the  whole 
thing.  So,  the  coarser  the  grinding  the  better  these  water  separation 
processes  were,  the  greater  the  difference  in  specific  gravity.  But 
what  you  ran  up  against  there  was  the  fact  that  in  the  heart  of  a  grain 
of  gangue  there  might  be  a  particle  of  metal,  and  you  have  lost  it  by 
not  grinding  fine.  So  there  the  millers  were  between  the  Devil  and 
the  deep  sea. 


MR.  KENYON  :  It  has  been  shown  that  the  processes  of  the  patents 
in  suit  depend  in  part  at  least  upon  certain  simple  facts  of  physical 
science  that  are  observable  to  the  knowing  eye,  and  that  clearly  dis- 
tinguish them  from  the  prior  art.  We  have  shown  that  these  processes 
are  not  oil-foam  or  oil-froth  processes,  or  oil-emulsion  processes,  or 
aerated  oil-flotation  processes  in  any  proper  sense,  but  are  processes 
of  air-flotation:  processes  that  effectively  evoke  the  power  of  air  to 
select  out  the  metal  from  the  gangue  in  a  freely  flowing  pulp,  and  to 
float  it  to  and  through  the  surface  for  separation. 

Air  has  little  affinity  for  oil  as  such,  and  air-bubbles  do  not  readily 
attach  themselves  to  oil  globules,  and  have  slight  lifting  power  when 
so  attached.  If  a  particle  of  mineral  lies  entrapped  in  an  oil  globule, 
or  has  an  oil  globule  attached  to  it,  an  air  bubble  coming  in  contact 
with  the  oil  globule  will  take  away  a  portion  of  the  oil,  but  will  have 
little  tendency  to  attach  itself  to  the  mineral.  Therefore,  while  air 
bubbles  may  be  mechanically  caught  and  entrapped  in  oil,  and  may 


198  THE  FLOTATION  PROCESS 

in  that  way,  increase  and  greatly  increase  the  mass  buoyancy  of  the 
oil,  that  is,  its  power  to  raise  mineral  particles  that  are  also  caught 
and  entrapped  within  it,  this  action  of  the  air  (which  had  been  sug- 
gested in  the  oil-foam  processes  of  the  prior  art)  is  not  secured  unless 
the  amount  of  oil  is  sufficient  and  the  character  of  oil  suitable  to  so 
mechanically  embrace  and  entrap  both  air  and  mineral.  That  is,  the 
oil  must  be  viscous. 

Air  has  a  powerful  affinity  for  clean,  metallic,  sulphide  surfaces. 
This  affinity  is  defeated  for  all  practical  ore  concentration  purposes 
in  the  mill  when  the  mineral  surfaces  are  coated  with  so  much  oil  as 
to  exhibit  the  physical  properties  of  oil  as  such,  such  as  adhesion  to 
other  similar  oiled  mineral  surfaces,  as  in  the  Cattermole  process,  or 
adherence  to  an  oil  lake  or  to  an  oil  foam  mass  and  resultant  buoy- 
ancy flotation,  as  in  the  Elmore  process,  the  California  Journal 
process,  and  so  forth.  But  when  the  film  of  oil  on  the  metallic  sur- 
faces is  extremely  attenuated  (as  when  1%  of  oil  to  ore  is  employed) 
the  affinity  of  air  for  metal  is  not  merely  undefeated;  it  seems  to  be 
positively  increased  (why,  we  do  not  know)  so  that  for  all  practical 
ore  concentration  purposes  in  the  mill  the  attachment  will  persist  in 
and  out  of  the  pulp,  and  will  survive  any  amount  of  excess  agitation 
or  of  excess  aeration  in  the  pulp. 

Air  bubbles  have  vastly  greater  lifting  power  for  metal  particles 
than  oil  globules  have,  and  especially  the  sort  of  air  bubbles  that  are 
produced,  either  by  agitation  or  by  aeration,  in  water  modified  by  the 
reagents  of  the  patents  in  suit. 

Air  bubbles  in  unmodified  water,  however  produced,  progressively 
and  rapidly  coalesce,  and  with  explosive  violence,  which  tends  to  ex- 
plain the  fact  that  such  air  bubbles,  namely  in  unmodified  water,  will 
not  practically  concentrate  ore. 

Air  bubbles  in  pulp  modified  by  the  reagents  of  the  patents  in 
suit  have  an  enhanced  selective  affinity  for  metal  over  gangue  (why, 
we  do  not  know),  and  a  persistence  of  life  as  bubbles  in  the  pulp 
and  a  persistence  of  attachment  to  contacting  metal  particles  in  and 
out  of  the  pulp  sufficient  (but  why,  again,  we  do  not  know)  to 
permit  in  practice  of  ready  separation  and  removal,  and  to  result 
thereby  in  effective  ore  construction. 

THE  COURT:  You  say  "Why,  we  do  not  know."  Is  there  any 
theory  on  that  subject? 

MR.  KENYON  :    We  have  presented  no  theory. 

THE  COURT  :    You  have  no  theory  ? 

MR.  KENYON:    We  have  no  theory.     Dr.  Sadtler  says  variation 


AIR-FROTH    FLOTATION II  199 

of  surface  tension  explains  the  phenomenon,  but  how  I  do  not  know. 
I  do  not  know  how  variation  of  surface  tension  can  enhance  selective 
affinity,  or  how  it  can  explain  persistence  of  life  as  bubbles  in  and 
out  of  the  pulp,  or  how  it  can  explain  persistence  of  attachment  to 
contacting  metal  particles  in  and  out  of  the  pulp,  to  such  a  degree 
that  practical  ore  concentration  in  a  mill  is  an  accomplished  fact. 

Whatever  the  explanation  of  the  phenomena  involved,  it  is  clear 
that  the  operation  proceeds  by  contact  of  air  and  metal  in  a  freely 
flowing  pulp  under  circumstances  conditioned  by  the  presence  of 
the  reagents  of  the  patents  in  suit,  and  opportunity  of  flotation 
after  contact. 

THE  COURT  :  You  say  the  contact  between  the  air  and  the  mineral 
particles  ? 

MR.  KEN  YON  :    In  the  pulp. 

THE  COURT:  Now,  if  the  mineral  particle  has  a  film  of  oil,  no 
matter  how  thin,  how  is  there  any  actual  physical  contact  between 
the  air  and  that  particle? 

MR.  KENYON:  The  mystery  of  the  thing  is  that  when  the  oil 
film  of  the  attenuated  character  that  is  produced  with  one-tenth  of 
1%  of  oil  to  the  ore,  when  that  film  is  present  on  the  metal  particle, 
the  air  particle  has  an  enhanced  appetite  for  it,  seeks  it  with  increased 
avidity,  instead  of  with  diminished  or  defeated  avidity  such  as  a 
thicker  film  will  produce. 

THE  COURT:    And  it  seeks  it  through  that  very  thin  film? 

MR.  KENYON  :  Seeks  it  through  that  very  thin  film,  as  it  were — 
that  helps. 

THE  COURT:  Not  through  the  actual  contact,  but  through  the 
film  being  so  very  attenuated,  it  seeks  the  metal  particle,  and  the 
interposition  of  the  film,  far  from  lessening  the  selective  action  of 
the  air  for  the  metal,  enhances  it — is  that  right? 

MR.  KENYON:  Yes,  that  is  right,  and  Dr.  Sadtler  on  the  stand 
suggested  an  idea  that  may  help  a  little.  He  said. that  an  attenuated 
film  of  that  kind  might  possibly  be  conceived  of  as  smoothing  the 
roughness  of  the  surface  of  cleavage  of  the  sulphide  particles. 

MR.  WILLIAMS  :     That  was  Dr.  Liebmann. 

MR.  KENYON:    Dr.  Liebmann? 

THE  COURT:    Increasing  the  effect? 

MR.  KENYON:  Increasing  the  attachment  or  appetite  of  the 
air  bubble  for  that  surface  so  smoothed. 

MR.  WILLIAMS  :    In  fact,  they  both  suggested  it. 

MR.  KENYON:    Yes,  Dr.  Liebmann  also  suggested  that  idea;  and 


200 


THE   FLOTATION    PROCESS 


Mr.  Dosenbach,  as  I  remember,  said  that  when  these  particles  had 
rough  surfaces  the  air  bubble  woujd  not  hold  them.  It  is  the  smooth 
surface  that  the  air  bubble  gets  its  grip  on.  Now,  this  microscopic 
film  of  oil  may  fill  up  microscopic  cavities,  may  bridge  over  micro- 
scopic roughnesses,  may  make  smooth  what  was  before  rough,  and 
in  that  way  enhance  the  avidity  of  the  air  particle  for  it,  and  the 
grip  of  the  air  particle  upon  it;  but  I  present  that  with  diffidence. 
That  is  a  matter  of  speculation. 


FlG.    41.      THE    QABBETT    MIXER. 

REDUCED    FACSIMILE    OF   DRAWING   IN   E.    R.    GABBETT'S    PATENT    NO.    444,345,    OF 

JANUARY    6,    1891. 


AIR-FROTH    FLOTATION II  201 

THE  COURT:  You  have  the  evidence  on  both  sides  for  that,  so  I 
do  not  suppose  counsel  on  either  side  will  contest  it. 

MR.  KENYON  :  That  is  so,  but  with  all  respect  to  both  witnesses, 
I  present  the  suggestion  with  diffidence. 

But  now  let  me  state  again  what  are  the  clear  essentials  from 
the  point  of  view  of  operation,  whatever  the  explanation  of  phenomena. 
Whatever  the  explanation  of  the  phenomena  involved,  it  is  clear 
that  the  operation  proceeds  by  the  contact  of  air  and  metal  in  a 
freely  flowing  pulp  under  circumstances  conditioned  by  the  presence 
of  the  reagents  of  the  patents  in  suit,  and  opportunity  of  flotation 
after  contact.  You  have  got  to  bring  your  bubble  and  your  metal 
particle  into  contact  in  this  freely  flowing  pulp,  and  under  circum- 
stances conditioned  by  the  presence  of  the  reagents  of  the  patents 
in  suit.  But  to  have  brought  them  into  contact — that  is  not  enough. 
There  must  be  another  factor,  namely,  opportunity  of  flotation  after 
contact,  so  that  you  may  separate — flotation  up  in  the  pulp  and 
through  the  surface  of  the  pulp — so  that  you  may  practically 
separate  them. 

THE  COURT  :    Those  are  essentials  in  the  flotation. 

MR.  KENYON:  Those  are  the  sine  qua  nwis,  and  those  are  the 
only  sine  qua  nons  if  we  have  presented  the  proper  theory  of  operation. 

And  as  to  apparatus,  it  is  clear,  too,  that  apparatus  for  efficiency 
bringing  about  in  a  freely  flowing  pulp  the  contact  of  air  and  metal 
under  the  conditions  stated,  and  for  permitting  or  assisting  flotation 
after  contact,  is  all  that  is  required. 

It  has  been  shown  not  only  that  the  fine  and  slime  that  were 
practically  unconcentratable  in  the  prior  art,  except  perhaps  by 
Cattermole — I  say  'perhaps'  because  Cattermole  never  reached  the 
mill.  On  the  threshold  of  the  mill  the  life  of  the  Cattermole  process 
was  cut  off  by  this  greater  child  of  the  brains  of  Sulman,  Picard, 
and  Ballot. 

It  has  been  shown  not  only  that  the  fine  and  slime  that  were 
practically  unconcentratable  in  the  prior  art  (except  perhaps  by 
Cattermole)  can  be  successfully  concentrated  by  the  processes  in 
suit,  but  also  that  the  presence  of  such  fine  and  slime  in  the  pulp 
actually  assists  the  concentration  of  the  ore,  and  is  indeed  almost 
essential  to  practical  success;  so  much  so  that  the  art  of  grinding 
has  been  revolutionized  where  the  processes  in  suit  are  employed 
and  fine  grinding  has  become  the  rule,  where  before  it  would  have 
been  the  ruin,  of  the  mill. 

The  history  of  what  happened  in  the  practical  art  before  the 


202  THE  FLOTATION  PROCESS 

inventions  in  suit  were  made,  and  of  what  has  happened  in  the 
practical  art  since  that  time,  shows  that  while  ways  and  means  of 
bringing  about  contact  of  air  and  metal  in  the  pulp  and  of  permitting 
or  assisting  flotation  after  contact  may  be  widely  varied,  the  success 
of  the  process  is  sharply  conditioned  within  relatively  narrow  limits 
in  the  matter  of  the  quantity  of  reagent  employed,  when  that  reagent 
is  the  oil  of  the  first  patent.  Especially  is  this  true  and  crucial  in  the 
case  of  the  first  patent  in  suit,  since  it  has  been  demonstrated  beyond 
dispute  that  any  notable  increases  of  oil  above  the  minute  propor- 
tion there  specified  practically  defeats  the  end  in  view  and  would 
in  the  mill  practically  prevent  the  concentration  desired,  and  would 
be,  not  only  intolerable,  as  a  dirty  and  utterly  non-controllable  mill 
operation,  but  impossible,  as  giving  a^treatly  enhanced  cost  a  greatly 
depleted  and  inferior  product.  ***j|B 

Now,  why  the  bubbles  have  enhanced  selective  affinity  for  metal 
over  gangue,  and  why  they  have  enhanced  persistence  of  life  as 
bubbles  in  and  out  of  the  pulp,  no  one  really  knows.  No  one 
really  understands  today  why  the  process  works  as  it  does  work. 
Under  such  circumstances  prevision  was  impossible.  And  where 
prevision  is  impossible,  nothing  can  anticipate  except  the  very  thing. 

THE  COURT  :  That  would  indicate  that  this '  was  a  discovery 
rather  than  an  invention  of  a  process. 

MR.  KENYON  :  Yes.  It  started  with  a  discovery.  As  a  process  it 
became  an  invention. 


CYANIDE   TREATMENT   OF   FLOTATION   CONCENTRATE  203 

CYANIDE  TREATMENT  OF  FLOTATION  CONCENTRATE 

By  CHARLES  BUTTERS  AND  J.  E.  CLENNELL 

(From  the  Mining  and  Scientific  Press  of  November  20,  1915) 

When  Charles  Butters  began  to  take  up  the  work  of  flotation 
in  our  Oakland  laboratory,  one  of  the  first  points  brought  to  our 
attention  was  the  treatment  of  the  concentrate  produced  by  flotation ; 
J.  E.  Clennell  was  accordingly  instructed  to  undertake  the  researches 
detailed  in  the  present  paper. 

The  whole  value  of  the  process  hinges  on  two  points,  namely, 
the  grade  of  tailing  produced  and  the  net  realization  of  the  value 
contained  in  the  concentrate,  these  two  considerations  being  of 
equal  importance.  This  last  point  is  complicated  by  questions  of 
geographical  situation,  for  if  the  concentrate  cannot  be  treated  locally 
the  cost  of  realization  may  be  so  heavy  that  flotation  would  be  entirely 
precluded. 

The  results  obtained  in  our  laboratory  by  the  combination  of 
flotation  and  cyanide  have  been  so  remarkable  that  a  serious  study 
of  the  disposal  of  concentrates  has  been  forced  upon  us. 

The  difficulties  attending  the  treatment  of  concentrate  by  cyanide 
are  well  known.  The  process  of  concentration  collects  in  a  small 
bulk  not  only  the  valuable  constitutents  of  the  ore  but  also  those 
substances  that  act  as  cyanicides,  or  which  are  readily  converted 
by  oxidation  or  otherwise  into  cyanicides,  so  that  their  influence, 
per  ton  of  material  treated,  is  greater  than  would  be  the  case  with 
the  unconcentrated  ore.  Heavy  minerals  such  as  the  sulphides  of 
iron,  copper,  lead,  arsenic,  antimony,  zinc,  and  double  sulphides  such 
as  mispickel,  proustite,  pyrargyrite,  and  bornite,  naturally  tend  to 
accumulate  in  the  concentrate.  If  some  interval  elapses  between  the 
formation  of  this  concentrate  and  its  treatment,  oxidation  may  take 
place,  with  formation  of  sulphates,  arsenates,  and  antimonates,  which 
are  still  more  detrimental  to  cyanide  treatment  than  the  original 
minerals.  These  difficulties  have  been  wholly  or  partly  overcome 
by  the  adoption  of  modifications  in  the  treatment,  such  as  preliminary 
water,  acid,  or  alkali  washing,  roasting,  fine  grinding,  the  use  of 
special  solvents,  such  as  bromo-cyanide,  and  prolonged  contact  of 
the  material  with  cyanide,  extending  in  some  cases  to  over  a  month. 

In  the  case  of  concentrate  produced  by  flotation,  the  minerals 
composing  the  product  are  substantially  the  same  as  those  obtained 
by  gravity  concentration,  consisting  of  the  sulphides  and  double 


204  THE  FLOTATION  PROCESS 

sulphides  of  the  heavy  metals,  and  it  is  to  be  expected  that  the 
same  difficulties  will  be  encountered  in  their  treatment.  But  as  the 
concentrate  also  contains  a  considerable  part  of  the  oil,  tar,  or 
other  flotation  agent,  the  presence  of  this  foreign  matter  must  be 
taken  into  account.  In  some  cases,  this  circumstance  introduces  an 
additional  difficulty.  A  part  of  this  organic  matter  is  soluble  in  the 
cyanide  or  alkali  used  in  the  process,  and  the  solution  so  formed 
may  be  capable  of  absorbing  oxygen.  The  effect  produced  by  car- 
bonaceous matter  in  precipitating  gold  and  silver  previous^  dissolved 
by  cyanide  is  well  known  and  has  been  a  source  of  much  trouble  in 
many  localities.  Some  of  the  constituents  of  this  matter  are  not 
easily  eliminated  and  appear  to  resist  oxidation  even  at  a  high 
temperature ;  roasting  under  ordinary  conditions  does  not  completely 
remove  the  carbon;  it  is  probable  that  a  portion  derived  from  tar 
remains  in  the  graphitic  form,  capable  of  acting  as  a  precipitant  for 
gold  or  silver. 

The  experiments  detailed  below  were  made  on  concentrates  pro- 
duced from  typical  gold  and  silver  ores  by  a  modified  type  of  the 
Minerals  Separation  flotation  machine.  Most  of  the  tests  were  made 
in  neutral  or  alkaline  media.  The  frothing  agents  employed  were 
those  in  general  use,  consisting  of  tar,  creosote,  carbolic  acid,  pine-oil, 
and  fuel-oil.  It  is  not  proposed  to  discuss  these  in  detail  in  the 
.present  paper;  it  will  be  sufficient  to  state  that  the  concentrate  was 
collected  •  and  drained  on  a  vacuum-filter  and  in  some  cases  dried 
at  a  moderate  temperature  before  treatment. 

As  an  example  of  an  ore  in  which  the  value  consists  essentially 
of  gold  we  may  take  the  product  of  the  San  Sebastian  mine,  in 
Salvador,  operated  by  the  Butters  Salvador  Mines,  Ltd.  For  pre- 
liminary work  a  composite  sample  was  made  from  21  lots  taken 
from  different  parts  of  the  mine,  and  concentrate  produced  by 
treating  the  finely  crushed  ore  in  a  10-lb.  flotation  machine.  The 
sample  taken  for  this  test  assayed  originally  1.54  oz.  gold  and  0.28  oz. 
silver.  The  concentrate  obtained  by  flotation  assayed  4.92  oz.  gold 
and  1.14  oz.  silver.  As  this  constituted  25%  of  the  weight  of  ore 
taken,  the  gold  recovered  in  the  concentrate  amounted  to  79.9%  of 
the  total.  An  analysis  of  the  concentrate  showed : 

%  % 

Insoluble    44.3      Iron   24.3 

Sulphur    26.2      Copper    0.8 

together  with  small  quantities  of  molybdenum,  tellurium,  and  other 
elements.  The  tailing  carried  0.04  oz.  gold  per  ton. 


CYANIDE   TREATMENT    OF    FLOTATION    CONCENTRATE 


205 


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206  THE  FLOTATION  PROCESS 

The  first  tests  were  made  with  the  object  of  determining  whether 
this  material  could  be  treated  advantageously  raw  by  agitation  with 
cyanide.  In  addition  to  direct  cyanide  treatment  various  modifica- 
tions were  tried,  as  shown  in  Table  I,  including  addition  of  lead 
acetate,  preliminary  alkali  treatment,  desulphurizing  with  alkali  and 
aluminum,  and  bromo-cyanide.  The  last  procedure  showed  a  marked 
improvement  over  every  other  method  of  raw  treatment,  but  still 
failed  to  yield  a  satisfactory  extraction.  The  extraction  was  increased 
by  increasing  cyanide  strength,  but  with  strong  solution  the  con- 
sumption of  cyanide  became  prohibitive,  and  alkaline  sulphides  were 
formed.  This  effect  can  be  prevented  and  cyanide  consumption 
much  reduced  by  addition  of  lead  acetate,  some  improvement  in 
extraction  being  obtained.  Preliminary  alkali  treatment  with  or 
without  aluminum  showed  no  benefit  whatever.  The  fact  that  bromo- 
cyanide  has  a  marked  effect  on  the  extraction  suggests  that  a  portion 
of  the  gold  may  be  present  as  a  telluride.  This  conclusion  is  supported 
by  experiments  made  by  direct  treatment  of  the  original  ore,  without 
concentration;  these  tests  showed  that  a  certain  proportion  of  the 
gold  is  inaccessible  to  cyanide  even  after  very  fine  grinding  and 
prolonged  contact.  (See  Table  XL) 

As  these  results  did  not  appear  encouraging  for  any  system  of 
raw  treatment,  attention  was  next  turned  to  roasting.  It  was  soon 
found  that  roasting  within  certain  limits  of  temperature  converted 
a  considerable  part  of  the  copper  into  sulphate,  which  could  be 
leached  with  water,  together  with  some  sulphate  of  iron,  leaving  the 
residue  in  a  favorable  condition  for  cyanide  treatment.  Preliminary 
acid  wash  of  the  roasted  material  was  also  tried;  this  would  have 
the  advantage  of  dissolving  a  further  quantity  of  copper  that  might 
have  become  converted  into  oxide  in  the  roasting,  but  the  results 
show  that  the  benefit  obtained  would  not  warrant  the  additional  cost. 
Another  test  was  made  in  which  the  concentrate  was  cyanided  raw 
before  roasting  and  acid-washing,  and  re-cyanided  after  the  washing : 
this  also  showed  no  advantage  either  in  extraction  or  cyanide  con- 
sumption over  direct  roasting,  water-wash,  and  cyanide.  In  all  cases 
the  roasted  material  was  agitated  with  cyanide,  using  a  dilution 
of  3:1.  The  results  obtained  by  these  three  methods  are  shown  in 
the  following  table.  (No.  II.) 

In  Test  No.  2  the  acid-washing  was  made  with  1%  H2S04,  using 
approximately  5  tons  of  wash  per  ton  of  concentrate  treated.  Before 
agitation  with  cyanide,  the  pulp  was  re-ground  in  a  model  tube-mill 
with  glass  marbles. 


CYANIDE   TREATMENT    OF    FLOTATION    CONCENTRATE 


207 


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208  THE  FLOTATION  PROCESS 

In  Test  No.  3  the  preliminary  raw  treatment  was  made  with 
0.1%  KCN  using  a  dilution  of  2:1,  for  two  days;  the  extraction 
of  gold  was  12%.  Acid  treatment  was  made  with  1%  H2S04, 
dilution  1 : 1,  agitated  18  hours,  and  then  leached  with  water  before 
cyaniding.  Roasted  and  washed  concentrate  agitated  with  cyanide 
for  4  days. 

Test  No.  1  on  Table  II  indicates  that  the  flotation  concentrate 
from  the  San  Sebastian  ore  may  be  successfully  treated  by  a  simple 
process  of  roasting,  water-washing,  and  cyaniding.  This  conclusion 
was  confirmed  by  numerous  experiments  on  a  large  scale  in  which 
the  material  was  roasted  in  a  hand-reverberatory  furnace,  and  the 
roasted  product  treated  by  agitation  in  tanks  with  mechanical 
stirrers,  adding  water,  settling,  and  decanting  until  the  bulk  of  the 
copper  and  iron  salts  was  removed,  finally  collecting  the  material 
on  a  vacuum-filter  and  washing  on  the  filter  to  remove  the  last 
traces  of  soluble  salts.  The  washed  concentrate  was  then  re-pulped 
with  lime  and  cyanide  solution  in  an  agitation-tank,  and  treatment 
continued  in  the  ordinary  way.  The  results  of  the  bottle  tests  were 
fully  confirmed. 

Attempts  to  treat  the  material  by  percolation  were  not  successful. 
Owing  to  the  fine  grinding  of  the  ore  previous  to  flotation,  the  roasted 
material  showed  a  tendency  to  slime;  percolation  took  place  slowly 
and  irregularly,  through  channels  formed  in  the  mass,  so  that  the 
extraction  by  this  means  was  always  imperfect. 

In  the  tests  made  in  the  large  muffle  the  oxidation  was  somewhat 
more  effective,  but  a  rather  longer  time  was  required  to  reach  the 
temperature  at  which  roasting  began.  Temperature  was  approxi- 
mately determined  by  Seger  cones. 

On  examining  the  details  of  Table  III,  it  will  be  apparent  that 
the  most  favorable  results  were  obtained  when  roasting  was  carried 
out  at  a  low  temperature ;  under  these  conditions  a  maximum  amount 
of  copper  was  extracted  by  water-washing,  and  the  highest  extraction 
of  gold  obtained  with  a  minimum  cyanide  consumption. 

In  this  ore  the  silver  is  negligible,  but  it  is  significant  that  the 
silver  extraction  on  the  roasted  material  is  poor  in  all  cases.  This 
condition  will  be  noted  in  most  cases  where  attempts  have  been  made 
to  treat  silver  ores  by  cyanide  after  an  oxidizing  roast. 

With  these  results  as  a  guide,  tests  were  made  on  a  larger  scale 
on  the  same  material,  roasted  by  hand  in  an  oil-fired  reverberatory 
furnace.  A  charge  of  about  400  Ib.  was  dried  slowly  in  a  sample 
drier,  and  charged  into  the  furnace;  the  temperature  was  gradually 


CYANIDE    TREATMENT    OF    FLOTATION    CONCENTRATE 


209 


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THE   FLOTATION   PROCESS 


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CYANIDE   TREATMENT    OF    FLOTATION    CONCENTRATE  211 

raised  till  it  approximated  that  obtained  in  the  muffle-roasts,  probably 
about  550°  C.  After  3J  hours,  the  flame  was  turned  off  and  the 
charge  allowed  to  cool  in  the  furnace  over-night.  The  concentrate 
roasted  in  this  way,  showed  little  or  no  tendency  to  sinter  or  form 
lumps,  but  in  subsequent  tests  when  the  material  was  charged  without 
previous  drying,  portions  of  the  concentrate  agglomerated  into  com- 
paratively hard  lumps,  which  contained  a  core  of  unroasted  material, 
and  which  it  was  necessary  to  sift  out  and  re-roast  after  grinding. 
Possibly  in  practice  it  would  be  advisable  to  pass  the  material,  after 
drying  and  before  roasting,  through  a  ball-mill  or  similar  pulverizer. 

A  bottle-test  made  on  a  scale  of  100  gm.  on  a  sample  of  roasted 
concentrate  from  the  above  reverberatory  charge  showed  the  following 
results : 

TABLE  IV 

Copper  extracted  per  cent  of  raw  concentrate: 

By  water-wash 0.435 

By  cyanide 0.039 

Total    0.474 

Cyanide  consumed  per  ton  of  washed  concentrate 5.03  Ib. 

Cyanide  consumed  per  ton  of  raw  concentrate 4.21  Ib. 

Under  cyanide  treatment  3  days 

1  ton  raw  concentrate  =  0.837  ton  washed. 

Gold,  Silver, 

Oz.  Oz. 

Assay  of  roasted  concentrate  3.70  0.86 

Assay  of  washed  concentrate  3.90      .          0.94 

Assay  of  washed  concentrate  calculated  on  raw  concentrate  3.26  0.79 

Loss  per  ton  of  raw  concentrate 0.24  0.10 

Residue  assay  on  washed  concentrate 0.05  0.60 

Residue  assay  calculated  on  raw  concentrate 0.04  0.50 

%  % 

Extraction  on  roasted  and  washed  concentrate 98.7  36.2 

Extraction  calculated  on  raw  concentrate 98.9  43.8 

Recovery  calculated  on  raw  concentrate 92.0  32.6 

The  loss  shown  in  this  test  seems  to  be  mostly  mechanical,  due 
to  dust  carried  off  while  stirring  the  charge;  it  could  probably  be 
much  reduced  by  using  a  suitable  roaster  with  revolving  rabbles  and 
a  dust-chamber. 

AGITATION  TESTS 

The  following  tests  were  made  in  small  tanks  fitted  with  wooden 
paddles. 

No.  1.    Agitated  with  cold  water,  washed  by  settlement  and  decan- 


212 


THE   FLOTATION   PROCESS 


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CYANIDE  TREATMENT  OF  FLOTATION  CONCENTRATE 


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218  THE  FLOTATION  PROCESS 

tation,  then  drained  by  vacuum  on  a  horizontal  filter-tray ;  re-pulped 
with  lime  and  cyanide  solution. 

No.  2.  Agitated  with  hot  water,  washed  by  settlement  and  decan- 
tation,  neutralized  with  lime  and  agitated  with  cyanide  without 
previous  filtration.  Cyanide  treatment  by  deeantation,  finally  washing 
without  water. 

PERCOLATION  TESTS 

Portions  of  the  same  roasted  charge  as  were  used  for  the  previous 
tests  were  leached  in  tanks  with  a  canvas  filter,  using  vacuum  to 
aid  filtration.  After  washing  out  soluble  salts  as  far  as  possible  in 
this  way,  the  residue  was  mixed  with  lime  and  treated  by  percolation 
with  cyanide  solution  in  the  same  manner. 

In  view  of  the  unsatisfactory  results  obtained  by  percolation  and 
the  fact  that  further  extraction  was  made  by  increased  water-washing, 
the  residue  of  charge  No.  1  was  mixed  with  the  residue  of  charge 
No.  1  treated  by  agitation  (see  Table  V)  and  the  united  charge 
agitated  further  with  water,  then  with  weak  cyanide  solution  and 
finally  with  water  again. 

The  result  of  these  tests  indicates  that  thorough  washing  is  essential 
for  a  high  extraction.  Filtration  without  vacuum  was  found  to  be 
practically  impossible. 

The  following  tests  were  made  on  another  portion  of  roasted 
concentrate,  to  determine  the  influence  of  cyanide  strength  on 
extraction.  Eight  tests  were  made;  in  the  first  four  a  preliminary 
wash  was  given  with  hot  salt  solution,  10%  NaCl  using  2  tons  of 
material  treated.  In  the  remaining  four  tests  the  preliminary  wash 
was  given  with  water  alone,  using  4  tons  per  ton  of  material.  The 
salt  wash  showed  some  extraction  of  silver,  but  it  does  not  appear 
that  any  advantage  derived  from  this  would  warrant  the  additional 
cost. 

The  cyanide  treatment  is  detailed  in  the  accompanying  tables : 

From  these  results  it  appears  that  the  extraction  is  scarcely 
affected  by  variation  of  cyanide  strength  within  the  limits  and  under 
the  conditions  of  the  tests.  The  cyanide  consumption,  however, 
increases  with  increasing  strength.  Apparently  the  best  results  are 
obtained  with  a  strength  of  0.125%  KCN. 

Two  tests  were  also  made  on  another  portion  of  roasted  concen- 
trate from  the  same  lot  of  ore  to  determine  the  influence  of  time 
on  the  cyanide  treatment. 

From  this  test  it  is  evident  that  the  gold  in  the  roasted  concen- 
trate is  rapidly  soluble  in  cyanide.  The  small  insoluble  portion 


CYANIDE   TREATMENT    OF   FLOTATION    CONCENTRATE 


219 


220  THE  FLOTATION  PROCESS 

seems  to  be  quite  inaccessible  to  prolonged  treatment  or  to  stronger 
solutions. 

The  foregoing  tests  sufficiently  indicate  that  the  San  Sebastian 
concentrate,  produced  by  flotation,  may  be  treated  successfully  on 
a  commercial  basis  by  the  method  of  roasting,  water- washing,  and 
cyaniding.  Some  tests  were,  however,  made  by  alternative  methods 
for  the  purpose  of  comparison. 

The  processes  thus  tried  were: 

1.  Chlorination  by  saturating  the  roasted  charge  with  chlorine 
gas  and  leaching  with  water,  as  in  the  old  Plattner  process. 

2.  Direct  cyanide  treatment  of  the  raw  ore  after  fine  grinding 
in  a  tube-mill  with  steel  balls. 

CHLORINATION  TESTS 

A  charge  of  roasted  concentrate  was  moistened  wtih  about  15% 
of  water,  and  placed  loosely,  without  any  paper  or  other  filter,  in  a 
porcelain  funnel  with  flat  perforated  diaphragm.  Chlorine  gas  was 
introduced  from  below  through  the  neck  of  the  funnel,  and  after 
saturation,  the  charge  was  allowed  to  stand  covered  for  24  hours. 
It  was  then  leached  out  with  water  and  the  residue  dried  and 
assayed.  The  extraction  was  found  by  difference  of  head  and  tail 
assays;  it  was  also  checked  by  precipitating  the  filtrate  with  ferrous 
sulphate,  allowing  to  settle  and  collecting  the  deposited  gold  on 
a  filter.  This  was  dried  and  cupelled. 

In  one  case  the  residue  after  chlorination  was  further  treated 
by  agitation  with  cyanide.  The  results  obtained  by  chlorination 
are  detailed  in  the  accompanying  table. 

The  residue  from  test  No.  3  (Table  X)  was  further  treated  by 
cyanide,  by  agitation  for  4  days  with  a  solution  originally  at  0.2% 
KCN,  and  increased  toward  the  end  of  the  treatment  to  0.5%  KCN, 
using  a  dilution  of  3 : 1.  This  treatment  yielded  the  following  results : 

Gold,  Silver, 

Oz.  Oz. 

Final  residue  after  cyanide  treatment 0.07  0.87 

%  % 

Extraction  from  chlorination  tailing 41.7  .  19.4 

Total  extraction  from  raw  concentrate 98.3  18.4 

From  these  figures  it  would  seem  that  the  results  to  be  expected 
from  chlorination,  or  from  chlorination  followed  by  cyanide,  are  in 
no  way  superior  to  those  obtainable  by  water-washing  and  cyanide. 
Either  method  will  give  a  satisfactory  extraction  and  the  choice 
would  depend  on  relative  cost  under  local  conditions. 


CYANIDE  TREATMENT  OF  FLOTATION  CONCENTRATE  221 

DIRECT  CYANIDING  OF  RAW  ORE 

It  is  interesting  to  compare  the  results  obtained  on  this  ore  by 
direct  cyaniding  without  any  form  of  concentration,  with  those 
given  by  the  combination  of  flotation  and  cyanide. 

The  following  tests  were  made  on  portions  of  the  same  lot  of 
ore  as  was  used  for  tests  detailed  in  the  preceding  tables.  Three 
charges  were  treated ;  the  first  two  were  taken  from  a  portion  crushed 
in  a  small  tube-mill  with  manganese-steel  balls,  using  the  following 
quantities : 

Ore,  25  Ib. ;  lime,  0.25  Ib. ;  water,  17  Ib. 

Time  of  grinding,  6  hours. 

The  pulp  was  drained  on  vacuum-filter  to  26.4%  moisture. 

The  third  test  was  made  on  part  of  a  larger  portion  of  ore  crushed 
in  the  same  manner,  but  in  a  larger  mill,  for  use  with  a  200-lb. 
flotation  machine. 

TABLE  XI 

DIRECT  CYANIDING  OF  RAW  ORE,  WITHOUT  CONCENTRATION 


Test  No.  1.     Test  No.  2.    Test  No.  3. 

Wet  weight  of  ore  taken  (gm.)  

708 

708 

100 

Dry  weight  of  ore  taken  (gm.)  

.  .  ,     521 

521 

95 

Solution  added    (cc.)  

1,457 

1,457 

300 

Lime  added,  per  ton  of  ore  (Ib.)  

, 

... 

21.1 

Strength  of  solution  maintained  at  KCN. 

.  .  .      0.1% 

0.2% 

0.2% 

Final  dilution  of  pulp  

3:1 

3:1 

3:1 

Time  under  cyanide  treatment  (days)  .  .  . 

5 

5 

3 

Cyanide  consumed  per  ton  of  ore  (Ib.)  .  .  . 

4.80 

6.32 

4.76 

Test  No.  1. 

Test  No.  2. 

Test. 

No.  3. 

Gold,         Silver, 

Gold, 

Silver, 

Gold, 

Silver, 

Oz.              Oz. 

Oz. 

Oz. 

Oz. 

Oz. 

Head  assay  0.625            0.16 

0.625 

0.16 

0.895 

0.13 

Residue  assay   0.205            0.07 

0.16 

0.04 

0.155 

Extraction  (%)    67.2            56.2 

74.4 

75 

82.7 

CYANIDE  TREATMENT  OP  FLOTATION  TAILING 

A  flotation  test  was  made  on  the  ore  used  in  Test  No.  3  (Table  XI) , 

resulting  as  follows: 

Percentage 

Assay-value.  of  total  value. 

Weight,  Gold,  Silver,  Gold,  Silver, 

Product.  %  Oz.  Oz. 

Head    0.895  0.13 

Concentrate   12.45  6.53  1.04  90.8  99.6 

Middling    11.45  0.35  4.5 

Tailing    76.10  0.055  ...  4.7 


222  THE  FLOTATION  PROCESS 

The  tailing  thus  produced  was  agitated  with  cyanide,  with  results 
as  shown  below: 

TABLE  XII 

CYANIDE  TBEATMENT  OF  RAW  FLOTATION  TAILING 
Wet  weight  of  tailing  taken,  100  gm. 
Moisture,  7.4%.    Dry  weight,  92.6  gm. 
Lime  added,  1  gm.  =  21.6  Ib.  per  ton  of  tailing. 
Strength  of  solution  maintained  at  0.2%  KCN. 
Dilution  of  final  pulp,  3:1. 
Time  under  cyanide  treatment,  3  days. 
Cyanide  consumed  per  ton  of  tailing,  1.40  Ib. 

Gold, 
Oz. 

Assay  before  cyaniding 0.055 

Assay  after  cyaniding 0.0125 

Extraction  77.3% 

COMPARISON  OP  METHODS 

For  the  sake  of  comparison,  we  may  assume  in  view  of  previous 
results  that  an  extraction  of  98%  could  be  obtained  from  the  concen- 
trate yielded  by  the  above  flotation  test,  by  the  method  detailed, 
namely,  roasting,  water-washing,  and  cyaniding.  The  values  shown 
in  the  middling  may  be  eliminated  on  the  assumption  that  in  practice 
the  middling  would  be  constantly  returned  to  the  head  of  the  machine, 
and  that  finally  only  two  products  would  be  obtained,  concentrate 
and  tailing,  having  the  same  assay- values  as  in  the  test.  The  result 
of  the  flotation  test  would  then  appear  as  follows: 

Percentage 

Assay-value.  of  total  value. 

Weight,  Gold,  Silver,  Gold,  Silver, 

Product.  %  Oz.  Oz. 

Concentrate  12.97  6.53  1.04  94.6  103.8 

Tailing    87.03  0.055  ...  5.4 

We  have,  therefore,  per  ton  of  raw  ore:          Gold,  Percentage 

Recovered  from  concentrate:  Oz.  Gold.       of  total  gold. 

6.53   X   0.1297  X  0.98     =  0.830  $17.16  92.7 

Recovered  from  tailing: 

0.055  X  0.8703   X   0.773  =  0.037  0.76  4.1 


Total  recovery   0.867  $17.92  96.8 

Heads    0.895  18.54  100 

Taking  the  figure  of  Test  No.  3    (Table  XI)    as  indicating  the 
possible  recovery  by  direct  cyanide  treatment  we  have: 


CYANIDE   TREATMENT    OF   FLOTATION    CONCENTRATE  223 

Gold,  Percentage 

Oz.  Gold.       of  total  gold. 

By  direct  cyaniding  0.74  $15.30  82.7 

Additional  recovery  by  combined  method..   0.127  2.62  14.1 

Per  ton  of 
concentrate. 

0.16  X  100 

Flotation,   16c.  per  ton  of  ore  =  =  $1.25 

13 

Roasting  1.00 

Extra  labor,  etc.,  in  cyaniding 0.50 

$2.75 

Per  ton  of  raw  ore,  2.75   X  0.1297 =     0.36 

Net  saving  by  combined  method 2.26 

In  addition  to  this  there  is  a  saving  in  cyanide  consumption  as 
follows,  per  ton  of  raw  ore : 

Cyanide 
consumed. 

By  direct  treatment 4.76  Ib. 

By  combined  treatment: 

Concentrate  (say,  5  Ib.  per  ton)  5  X  0.13 =  0.65  Ib. 

Tailing,  1.4   X   0.87 =  1.12 

1.77 

showing  a  saving  in  cyanide  of  2.99  Ib. ;  taking  cyanide  at  16c.  per  Ib. 
of  KCN  equivalent,  this  would  amount  to  48c.  per  ton  of  raw  ore 
treated,  bringing  the  total  saving  to  $2.74  or  about  $9600  on  a 
monthly  output  of  3500  tons. 

The  tests  given  in  Table  No.  Ill  show  that  about  0.4%  of  copper, 
or  8  Ib.  per  ton  of  raw  concentrate  (in  this  case  2  Ib.  per  ton  of 
raw  ore)  can  be  extracted  in  a  soluble  form,  and  might  be  recovered 
as  an  additional  source  of  revenue. 


224  THE  FLOTATION  PROCESS 

FLOTATION   ON   GOLD    ORES 

(From  the  Mining  and  Scientific  Press,  of  November  20,  1915) 
The  Editor: 

Sir — I  was  very  much  interested  in  the  interview  with  Mr.  Butters 
appearing  in  your  issue  of  August  21,  1915. 

Flotation  promises  in  the  future  to  take  a  very  important  part 
in  the  treatment  of  sulphide  gold  ores.  It  is  going  to  be  a  serious 
competitor  to  the  cyanide  process,  especially  where  the  precious  metals 
are  locked  up  within  the  sulphides.  At  the  present  time  there  are 
many  mills  treating  low-grade  gold  ores  in  California,  Alaska,  and 
Korea  that  employ  only  amalgamation  and  water-concentration 
(tables  and  vanners),  the  tailing  being  too  low  for  a  further  profit- 
able treatment  by  cyanidation. 

Concentration  results  will  no  doubt  in  the  future  be  improved 
by  the  application  of  flotation  to  the  treatment  of  the  slime.  The 
extraction  of  sulphides  from  the  sand  can  be  done  cheaply  and 
efficiently  on  Wilfley  or  Card  tables.  The  weakness  of  water- 
concentration  methods  during  the  past  has  been  with  the  treatment 
of  that  product  passing  a  200-mesh  screen  commonly  called  'slime.' 
The  best  concentrators  on  the  market  today  make  only  an  incomplete 
saving  of  the  fine  float  sulphide  mineral  which  in  many  cases  accounts 
for  a  good  part  of  the  gold  escaping  in  the  final  tailing.  Flotation 
is  the  remedy.  The  Suan  gold  mine  in  Korea  is  an  example. 

There  are  a  number  of  low-grade  sulphide  ores  (Oriental  Con- 
solidated in  Korea  and  the  Alaska  Tread  well)  that  do  not  require 
to  be  crushed  finer  than  25-mesh  in  order  to  free  the  sulphides  from 
the  gangue.  Would  such  a  coarse  product,  where  a  considerable 
portion  of  the  sulphide  remains  on  a  40  or  50-mesh  screen,  be  suit- 
able for  an  all-flotation  process?  I  am  inclined  to  favor  in  such 
cases  a  combination  process  consisting  of  tables  for  sand  and  flotation 
for  slime. 

Where  the  sulphide  minerals  are  finely  disseminated  throughout 
an  ore  and  comparatively  fine  grinding  is  necessary,  I  should  think 
an  all-flotation  process  would  then  be  in  order.  However,  those  of 
us  who  have  to  do  with  the  design  of  plants  would  insist  upon 
large-scale  tests  before  deciding  on  a  flow-sheet.  It  is  money  wisely 
spent  where  big  sums  of  money  are  involved  in  the  final  plant. 

A.  E.  DRUCKER. 
La  Salada,  Colombia,  October  9. 


THE  ELECTRICAL  THEORY  OF  FLOTATION  225 

THE  ELECTRICAL  THEORY  OF  FLOTATION 

By  THOMAS  M.  BAINS,  JR. 
(From  the  Mining  and  Scientific  Press  of  November  27,  1915) 

INTRODUCTION.  If  one  turns  to  'Elementary. Lessons  in  Electricity 
and  Magnetism/  by  Silvanus  Thompson  and  studies  the  fundamental 
principles  of  frictional  electricity,  as  given  in  Chapter  1,  a  clearer 
idea  of  the  causes  of  '  flotation '  may  be  obtained.  After  seeing  a 
few  experiments,  such  as  were  performed  at  the  Case  School  of 
Applied  Science  early  in  the  year,  it  is  not  a  difficult  matter  to 
believe  that  most  of  the  phenomena  are  electrical  in  nature.  For 
instance,  if  powdered  galena  ore,  with  a  limestone  gangue,  be  dropped 
into  pure  water,  most  of  the  powder  will  immediately  sink  to  the 
bottom.  As  the  air  enclosed  by  the  particles  is  expelled  gradually, 
one  sees  the  formation  of  'armored'  bubbles,  some  of  which  may  last 
for  days.  Here  is  flotation  without  oil  or  acid.  If  nitric  acid  is 
added,  the  gas  bubbles,  formed  by  the  action  of  the  acid  on  the 
gangue,  will  carry  up  particles  of  galena,  some  reaching  the  surface 
and  bursting,  while  others  too  heavily  loaded  with  galena  particles 
will  hover  just  below  the  surface.  These  will  form  clusters,  resem- 
bling bunches  of  grapes,  and  when  enough  gas  bubbles  join  the 
clusters,  they  start  upward  toward  the  surface,  but  generally  before 
reaching  there  they  are  overloaded  by  particles  falling  from  the 
bubbles  that  are  bursting  at  the  surface.  The  bubbles  with  their 
loads  often  resemble  balloons,  with  the  galena  hanging  on  to  the 
bottoms,  as  do  the  baskets  of  actual  balloons.  Some  of  the  bubbles 
will  be  completely  'armored'  while  others  will  be  nearly  free  from 
galena.  Another  experiment  that  may  be  successfully  used  in  the 
laboratory  for  the  flotation  of  the  difficult  sulphides,  such  as  old 
rusty  pyrite  concentrate,  like  sweepings  from  floors  of  old  mills, 
is  as  follows:  Mix  the  ore  with  bleaching  powder,  some  carbonate 
(say,  sodium  carbonate),  and  water.  Put  the  mixture  into  a  glass 
beaker  and  add  concentrated  nitric  until  red  nitrous  fumes  are 
given  off.  Chlorine  also  will  be  evolved.  The  bubbles  of  gas  are 
so  highly  charged  electrically  that  pyrite  from  the  Mother  Lode 
between  10  and  20-mesh  size  was  floated,  making  a  complete  separa- 
tion from  the  quartz  gangue.  In  this  experiment  the  nitrous  oxide 
was  the  active  agent,  for  if  the  same  experiment  is  conducted  with 
sulphuric  acid,  no  such  separation  takes  place.  Assayers  are  familiar 
with  a  similar  phenomenon  when  treating  blister  copper  with  concen- 


226  THE  FLOTATION  PROCESS 

trated  nitric  acid  and  heating.  Nitrous  oxides  are  formed  and  the 
metallic  copper  is  floated,  a  froth  of  copper  being  the  result.  Carbon 
dioxide  does  not  seem  to  be  as  active  as  the  nitrous  oxides  or 
chlorine  bubbles. 

ELECTRIFICATION  OF  THE  BUBBLE.  Two  different  substances, 
whether  gaseous,  liquid,  or  solid,  when  brought  intimately  into 
contact  and  moved  one  over  the  other,  always  produce  elec- 
trification. Difference  of  temperature  of  two  similar  substances 
in  frictional  contact  will  cause  electrification,  the  warmer  usually 
being  negatively  charged.  Something  certainly  happens  when  the 
surfaces  of  two  different  substances  are  brought  into  intimate  contact, 
for  the  result  is  that  when  they  are  drawn  apart,  they  are  oppositely 
charged.  The  nature  of  the  charge  depends  on  the  substances.  Fur 
rubbed  on  glass  electrifies  the  glass  negatively ;  while  if  glass  is  rubbed 
with  celluloid  it  will  become  charged  positively. 

A  blow  struck  by  one  substance  on  another  produces  opposite 
electrical  states  on  the  two  surfaces.  Again,  the  evaporation  of 
liquids  is  accompanied  by  electrification,  liquid  and  vapor  assuming 
opposite  charges,  though  this  is  only  apparent  when  the  surface  is 
in  agitation.  A  few  drops  of  copper  sulphate  thrown  on  a  hot 
platinum  plate  produces  violent  electrification,  as  the  copper  sulphate 
evaporates.  Electrical  charges  are  set  up  by  various  other  means, 
such  as  vibration,  disruption  of  material,  crystallization,  combustion, 
pressure,  and  chemical  reactions. 

It  would  seem  easier  therefore  to  electrify  a  bubble  than  to  keep 
it  from  being  electrified.  I  assume  that  the  bubbles  are  electrified, 
whether  by  means  of  air  being  forced  through  canvas,  by  beating 
air  into  water  with  blades,  or  by  other  means.  The  next  step  is  to 
consider  the  properties  of  an  electrified  sphere.  These  may  be  illus- 
trated by  suspending  two  light  spheres  of  conducting  materials  near 
each  other  by  means  of  silk  threads.  Upon  charging  the  spheres 
with  like  electric  charges,  they  will  repel  each  other,  but  if  a 
conductor  is  brought  toward  them,  both  are  attracted  to  the  conductor. 
Of  course,  if  the  spheres  touch  the  conductor  and  the  conductor  is 
grounded,  then  the  spheres  lose  their  charges.  If  the  conductor 
is  insulated  from  the  ground,  then  upon  contact  with  the  spheres, 
the  conductor  receives  a  similar  charge  and  the  spheres  will  be 
repelled.  Suppose  that  the  spheres  or  conductor  are  covered  with 
an  insulating  film.  Then  the  spheres  and  conductor  would  remain 
as  close  together  as  the  films  would  permit.  So  air  bubbles  that  are 
electrified  will  attract  conductors  near  them  that  are  free  to  move. 


THE  ELECTRICAL  THEORY  OF  FLOTATION  227 

Air,  being  a  poor  conductor  of  electricity,  the  bubbles  as  a  whole 
do  not  discharge  immediately  upon  contact  with  a  conductor.  The 
only  part  of  the  surface  discharged  is  that  in  immediate  contact 
with  the  conductor,  and  this  discharged  film  of  air  acts  as  a  dielectric 
and  non-conductor  to  the  rest  of  the  bubble,  which  remains  charged. 
The  amount  of  electrification  of  the  bubble  will  depend  on  various 
conditions,  such,  for  example,  as  the  amount  of  friction  produced 
by  the  blades  of  a  Minerals  Separation  machine.  Increase  the  speed 
and  the  electrification  is  greater  and  the  attraction  for  conductors 
will  increase,  reducing  the  proportion  of  conductors  in  the  tailing. 
Referring  to  D.  G.  Campbell's  article  in  the  Mining  and  Engineering 
World  of  January  17,  1914,  the  speed  of  agitation  and  the  percentage 
of  extraction  is  given  as  follows : 

Speed  of  blades,  Extraction,     Weight  of  product, 

r.p.m.  %  Gm. 

1800    68  39 

1200    54  32 

900 46  26 

600 39  18 

The  extraction  seems  to  vary  directly  as  the  square  root  of  the 
increase  in  speed.  But  it  will  be  observed  that  with  the  increased 
extraction,  the  percentage  of  sulphide  in  the  concentrate  decreases, 
due  to  the  attraction  of  the  small  particles  of  mixed  gangue  and 
sulphide.  If  the  bubbles  are  highly  charged,  the  concentrate  will 
not  be  as  clean  in  a  particular  case,  as  if  they  were  less  charged. 

Vapors  and  gases  may  be  highly  electrified.  The  Armstrong 
hydro-electric  machine,  devised  by  Lord  Armstrong,  gave  sparks  of 
5  to  6  feet.  The  friction  of  a  jet  of  steam  through  a  wooden  nozzle 
generates  the  charge  on  the  particles  of  condensed  water. 

RELATIVE  CONDUCTIVITY.  From  the  above,  it  appears  that  to 
float  a  mineral,  it  must  be  a  conductor.  The  following  table  of 
relative  conductivities  is  taken  from  Landolt-Bornstein  '  Physikalisch- 
Chemische  Tabellen,'  1912,  fourth  edition: 

Silver 681,000      Pyrite    41.7 

Copper    634,000      Magnetite    1.24 

Gold 455,000      Chalcopyrite   0.983 

Iron 113,000      Manganese    di-oxide 0.16 

Covellite     8,000       Cuprite    0.025 

Galena    3,350      Siderite    0.00014 

Graphite    700      Quartz    0.844xlO-n 

Pyrrhotite    119      Diamond    0.211X10-1* 

Chalcocite    .  91 


228  THE  FLOTATION  PROCESS 

From  this  table,  it  would  seem  that  the  metals  and  sulphides 
that  may  be  recovered  by  the  flotation  method  are  all  conductors. 
The  chalcopyrite  figure  seems  low,  but  the  flotation  properties  of 
sulphide  minerals  vary,  and  the  variation  in  the  conductivity  of 
the  different  minerals  may  have  something  to  do  with  this.  The 
better  the  conductivity  of  the  valuable  mineral,  the  easier  is  it  floated, 
other  factors  remaining  the  same. 

THE  INSULATING  FILM.  The  next  important  question  in  the 
problem  is  the  action  of  the  oils,  resins,  or  other  agents  now  used 
in  flotation.  Working  from  the  electrical  standpoint,  it  is  necessary 
to  prevent  the  charge  of  the  bubble  from  being  dissipated  and  thus 
breaking  down  the  froth,  before  it  has  done  its  duty.  Oils  and  other 
substances  have  a  tendency  to  coat  the  metals  and  minerals  that 
are  recovered  by  flotation,  and  if  the  air  bubble  is  completely 
surrounded  by  these  particles,  an  envelope  of  oil  or  other  dielectric 
will  insulate  the  bubble  and  prevent  the  dissipation  of  the  charge. 
Without  a  dielectric  film  about  the  bubble  no  permanent  froth  would 
be  formed.  It  is,  therefore,  necessary  to  add  some  material  of  great 
dielectric  strength  that  has  the  tendency  to  coat  the  valuable  mineral. 

The  words  'dielectrics'  and  'non-conductors*  or  'insulators'  should 
not  be  confused.  A  'dielectric'  is  a  substance  that  is  not  only  a 
non-conductor,  but  is  also  one  that  takes  part  in  the  propagation 
of  the  electric  inductive  forces.  All  dielectrics  are  'insulators,'  but 
equally  good  insulators  are  not  necessarily  equally  good  dielectrics. 
Air  and  glass  are  far  better  insulators  than  ebonite  or  paraffine, 
but  the  inductive  influence  acts  more  strongly  across  a  slab  of  glass 
than  across  a  slab  of  ebonite  or  paraffine  of  equal  thickness,  and 
better  still  across  these  than  across  a  layer  of  air  of  the  same 
thickness. 

It  may,  therefore,  be  possible  to  use  a  frothing  agent,  as  is  well 
known,  that  is  not  an  oil  at  all.  I  have  done  this  and  formed  froth 
that  has  lasted  for  weeks.  For  instance,  if  in  the  experiment 
mentioned  in  the  first  part  of  this  article,  with  galena  ore,  a  little 
alcohol  is  first  mixed  with  the  galena,  before  the  water  and  acid  is 
added,  then  a  heavy  mass  of  bubbles  and  galena  particles  will  be 
formed,  too  heavy  to  rise  to  the  surface. 

As  the  influence  of  the  charge  acts  inversely  as  the  thickness  of 
the  film,  it  is  imperative  that  some  dielectric  be  used  that  will  create 
a  very  thin  film  about  the  valuable  mineral.  The  dielectric  must 
also  be  of  such  a  character  as  to  aid  the  formation  of  a  great 
quantity  of  small  bubbles  in  the  liquid.  It  is  difficult  to  create  and 


THE  ELECTRICAL  THEORY  OF  FLOTATION  229 

maintain  small  bubbles  in  pure  water.    It  is  here  that  surface  tension 
phenomena  probably  play  a  part  in  flotation. 

ACIDITY  OF  THE  PULP.  In  Mr.  Campbell's  article  he  gives  the 
following  results  of  acid  variations : 

Acid,  Extraction,     Weight  of  product, 

Gm-  %  Gm. 

0.0  63  67 

0.2  50  60 

0.4  51  35 

0.4  48  30 

0.8  40  26 

Other  tests  also  show  that  the  extraction  decreases  as  the  acidity 
increases,  but  the  amount  of  gangue  in  the  concentrate  decreases 
much  more  rapidly.  With  an  acidified  pulp,  a  cleaner  concentrate 
is  obtained.  Also  better  results  are  obtained  if  the  acid  is  added 
before  the  oil  to  the  agitation-tank. 

As  to  the  action  of  acids  and  alkaline  substances  in  the  pulp, 
little  seems  to  be  known,  but  according  to  the  electrical  theory,  the 
addition  of  these  substances  causes  the  conductivity  of  the  pulp 
to  increase  greatly.  It  is  a  possibility  that  if  the  acid  is  not  added 
before  the  oil,  the  gangue,  oil,  and  conductors  are  all  electrically 
charged  by  reason  of  the  friction.  The  conductors  would  be  positively 
charged,  while  the  other  substances  and  the  air  bubbles  would  be 
negatively  charged.  If  the  pulp  is  a  poor  conductor,  as  it  would 
be  if  water  is  not  acidified  or  otherwise  made  a  conductor  (pure 
water  being  a  very  poor  conductor),  the  charges  on  the  gangue 
materials  would  remain  for  some  time  and  the  conductor  (sulphides, 
etc.)  would  attract  the  gangue  as  well  as  the  bubbles  and  oil,  thus 
causing  gangue  to  be  taken  up  with  the  bubbles.  By  the  addition  of 
acid,  the  charges  on  the  surface  of  the  solids  are  discharged  to  the 
ground,  and  the  bubbles  and  the  oil,  which  will  not  be  instantly 
discharged  as  are  the  solids,  will  attract  the  conductors. 

CONCLUSIONS.  It  might  be  stated  here  that  the  electrical  theory 
was  taught  last  year,  as  possibly  explaining  flotation  phenomena, 
to  the  class  in  ore-dressing,  at  the  Case  School  of  Applied  Science. 

The  above  mentioned  method  of  floating  conductors  may  be  used 
for  the  rapid  determination  of  certain  ingredients  in  ores  that  are 
amenable  to  the  flotation  process.  It  requires  only  a  beaker  and  a 
few  chemicals,  no  flotation  machines  being  needed.  For  the  rapid 
approximate  determination  of  insoluble  in  a  smelting  ore,  the  method 
will  give  a  fair  result  within  a  few  minutes.  If  the  conductor  is 


230  THE  FLOTATION  PROCESS 

readily  acted  upon  by  nitric  acid,  the  results  may  not  be  satisfactory, 
but  by  addition  of  oleic  acid  the  dissolving  action  of  the  acid  is 
reduced. 

The  following  summary  of  the  requirements  for  'flotation,'  con- 
sidered from  the  electrical  standpoint,  may  be  of  practical  use : 

1.  Ores  containing  valuable  minerals  or  metals  that  are  good 
conductors  are  the  only  ones  that  are  suitable  for  flotation. 

2.  To  buoy  these  conductors,  it  is  necessary  to  supply  enough 
electrified  bubbles  from  below  to  float  particles  of  the  conductors 
that  are  attracted ;  hence  the  smaller  the  bubble,  the  better  the  result, 
the  amount  of  gas  being  the  same. 

3.  Some  dielectric  fluid  is  necessary  to  cover  the  conductor  or  the 
bubble,  to  prevent  the  dissipation  of  the  electric  charge.    The  thinner 
the  film  of  dielectric  and  the  greater  its  dielectric  strength,  the  greater 
the  effective  attractive  force  and  the  more  permanent  will  be  the 
froth. 

4.  Some  material  must  be  added  to  the  water  to  increase  its 
conductivity,  to  obtain  a  clean  concentrate;  acids  in  small  quantity 
are  now  used. 


NOTES   ON    FLOTATION  231 

NOTES  ON  FLOTATION 

By  J.  M.  CALLOW 
(From  the  Mining  and  Scientific  Press  of  December  4,  1915) 

^HISTORICAL  SKETCH.  The  selective  action  of  oil  for  lustrous 
minerals  was  first  disclosed  by  Haynes  in  1860.  In  1885,  Carrie 
Everson  elaborated  this  idea  and  also  disclosed  the  fact  that  acid 
increased  the  so-called  selective  action.  Her  patent  called  for  oils, 
either  animal,  vegetal,  or  mineral,  and  also  an  acid  or  salt.  The 
process  was  tried  on  a  practical  scale  both  at  Baker  City  and  Leadville 
in  1889 ;  it  failed,  first,  because,  as  has  since  been  shown,  of  the  un- 
suitability  of  the  ore  to  flotation;  second,  because  her  invention  was 
too  far  in  advance  of  the  times.  Then  followed  the  Elmore  brothers, 
first  with  their  bulk-oil  process  and  later  with  their  vacuum  scheme. 
The  basic  principles  of  oil-flotation  were  undoubtedly  covered  by  the 
above  inventors  and  the  work  that  has  been  done  since  their  time  has 
been  merely  a  building  up  on  ground-work  laid  down  by  them.  Differ- 
ent kinds  of  oil,  different  quantities  of  oil,  and  all  the  varying  degrees 
of  agitation  were  all  exemplified  and  practised  by  them  in  one  phase 
or  another;  the  developments  that  have  since  been  made  are  but 
elaborations  of  the  fundamental  principles  laid  down  by  Haynes, 
Everson,  and  the  Elmore  brothers. 

In  1902  we  saw  the  development  of  the  Potter  or  Delprat  process 
in  Australia.  In  this  no  oil  was  used,  but  the  mineral  was  raised  by 
the  generation  of  gas,  brought  about  by  the  introduction  of  acid  in  the 
pulp  so  that  the  niineral  appeared  on  the  surface  of  the  separatory 
vessel  in  the  form  of  a  scum  or  froth  buoyed  by  minute  gas  bubbles 
attached  to  them,  and  thus  first  gave  the  suggestion  of  gaseous  flotation. 
In  1902,  also,  Froment,  an  Italian,  was  granted  a  patent  in  which  he 
combined  violent  agitation  with  oil  and  gaseous  flotation,  the  gas  being 
generated  within  the  pulp,  in  much  the  same  way  as  in  the  Potter- 
Delprat  process.  In  the  same  year,  Cattermole  came  out  with  a 
unique  scheme.  He  first  emulsified  his  pulp  with  a  small  quantity  of 
oil  by  violent  agitation  and  afterward  submitted  it  to  a  slow  stirring 
action  in  a  second  machine,  by  which  he  granulated  or  coagulated  the 
minerals  that  had  been  oiled  into  nodules,  which  he  afterward  sepa- 


*A  paper  originally  presented  at  the  annual  meeting  of  the  Utah  section 
of  the  American  Institute  of  Mining  Engineers,  at  Salt  Lake  City,  on  October 
4,  1915.  Read  at  the  New  York  meeting  in  February,  1916. 


232 


THE   FLOTATION   PROCESS 


FIG.  42. 


rated  from  the  pulp  by  gravity.  The  defect  of  this  process  was  that 
only  part  of  the  mineral  was  granulated,  the  rest  of  it  appearing  on 
the  surface  of  the  pulp  as  a  scum  or  froth,  and  so  was  lost  in  the 
tailing.  This  defect  of  the  Cattermole  process  suggested  the  funda- 


NOTES   ON    FLOTATION  233 

•P' 

mental  idea  of  the  process  afterward  described  by  Sulman,  Picard, 
and  Ballot  in  their  patents,  in  which,  instead  of  granulating  part  of 
the  mineral,  they  floated  all  of  it.  This  patent  forms  the  basis  of  all 
the  Minerals  Separation  operations.  It  was  first  exploited  in  Australia 
and  in  a  short  time  replaced  all  other  flotation  processes  in  that 
country. 

In  1904,  Macquisten  brought  out  his  tube  process,  a  very  in- 
genious scheme  which  gave  excellent  results  on  the  sandy  portion  of 
the  feed,  but  was  inoperative  when  slime  was  present.  This  was  a 
strictly  surface-tension  scheme,  and  its  inability  to  handle  slime  was 
a  serious  limitation. 

In  1912,  Hyde  introduced  a  modification  of  the  Minerals  Separa- 
tion process  into  the  mill  of  the  Butte  &  Superior  company,  at  Butte, 
Montana.  This  differed  from  the  regular  practice  in  that  it  in- 
troduced a  double  treatment,  first  ' roughing '  and  then  ' cleaning'  the 
concentrate. 

PNEUMATIC  FLOTATION.  Early  in  1909,  I  did  a  great  deal  of  work 
with  the  Macquisten  flotation  process  and  in  the  installation  of  the 
tube-plant  of  the  Morning  mill  at  Mullan,  Idaho.  This  work  was 
followed  by  a  large  amount  of  experimenting  on  the  different  kinds 
of  existing  flotation  processes,  the  outcome  of  which  was  the  develop- 
ment of  the  pneumatic  method. 

The  first  application  of  pneumatic  flotation  for  the  treatment  of  ore 
was  made  by  me  at  the  mill  of  the  National  Copper  Co.  at  Mullan. 
This  plant  was  designed  and  built  by  me  and  was  a  success  in  every 
way  from  the  very  start.  Construction  was  started  on  August  14, 

1913,  and  the  plant  went  into  successful  operation  about  April  10, 

1914.  The  flow-sheet  is  given  in  Fig.  42. 

Since  that  date,  the  method  has  been  adopted  by  nearly  all  the 
other  mills  in  the  Coeur  d'Alene  treating  lead  and  lead-zinc  ores, 
notably  the  Gold  Hunter,  Morning,  Hercules,  Bunker  Hill  &  Sullivan, 
Caledonia,  Last  Chance,  Hecla,  Standard,  etc.,  a  total  of  about  50 
cells  in  all,  treating  from  1500  to  2000  tons  of  slime  and  fine  sand  per 
day.  The  same  method  also  has  since  been  adopted  by  the  Inspiration, 
Arizona,  Anaconda,  Magma,  and  other  copper  companies,  and  by  the 
Silver  King,  Daly-Judge,  Duquesne,  and  El  Rayo  mining  companies, 
on  lead,  zinc,  and  other  ores,  making  a  total  of  some  680  cells  in  opera- 
tion or  in  the  course  of  erection,  having  a  combined  capacity  of  25,000 
to  28,000  tons  per  day. 

The  flow-sheets  of  the  Inspiration  and  the  Arizona  Copper  plants 
are  given  in  Fig.  43  and  44.  The  Daly-Judge  flow-sheet,  in  Fig:  45,  is 


234 


THE   FLOTATION    PROCESS 


FIG.  43. 


an  interesting  example  of  the  recoveries  possible  on  zinc-lead,  fine 
sand,  and  slime. 

The  accompanying  diagram,  Fig.  46,  illustrates  the  various 
elements  composing  the  Callow  method. 

A  is  a  mixer  operated  by  compressed  air  for  the  purpose  of  mixing 


NOTES   ON    FLOTATION  235 

and  emulsifying  the  oil,  the  air,  and  the  water,  the  same  type  of 
apparatus  being  in  common  use  in  cyanide  work.  In  cases  where  the 
oil  or  frothing  agent  can  be  fed  into  the  crushing  machine  or  tube- 
mill,  this  mixer,  or  Paehuca  tank,  can  be  eliminated,  so  that  the  oil  is 
fed  direct  into  the  mill  and  thence  into  the  separatory  cell. 

It  has  been  proved  conclusively  that  agitation  per  se  is  not  neces- 
sary to  successful  flotation  by  the  pneumatic  method.  In  one  of  the 
plants  a  Paehuca  mixer  for  each  four  roughing-cells  was  installed. 
This  received  the  thickened  feed  from  a  Dorr  tank,  which  feed  was 
elevated  by  a  belt-and-bucket  elevator.  The  oil  was  fed  into  the  boot 
of  the  elevator  and  the  mixing  there  served  all  purposes,  since  the 
results  without  the  Pachucas  were  found  to  be  just  as  good  as  with 
them.  Therefore  the  use  of  them  in  this  plant  has  been  abandoned. 

B  is  the  initial  or  roughing  separatory  cell.  It  consists  of  a 
tank  about  9  ft.  long  over  all  and  24  in.  wide,  with  a  bottom  inclined 
at  from  3  to  4  inches  of  fall  per  foot;  it  is  20  in.  at  the  shallow 
end  and  45  in.  deep  at  the  deepest  end.  It  may  be  built  of  either 
steel  or  wood,  preferably  wood. 

Fig.  47  and  48  show  the  cell  in  detail.  The  bottom  of  the  tank  con- 
sists of  a  porous  medium  made  of  four  thicknesses  of  loosely  woven 
canvas  twill,  properly  supported  by  a  backing  of  perforated  metal 
to  prevent  bulging  when  under  air-pressure.  Through  this  porous 
medium  compressed  air  is  forced  by  the  blower  E.  Porous  brick 
or  any  other  ceramic  material  may  be  used  to  ensure  the  necessary 
fine  subdivision  of  the  air.  Some  of  these  have  been  tried,  but  for 
practical  and  mechanical  reasons  the  loosely  woven  canvas-twill  seems 
to  serve  all  purposes  better  than  anything  else,  and  has  been  adopted 
as  the  standard  porous-bottom  construction. 

The  space  underneath  this  porous  medium  or  bottom  is  subdivided 
into  eight  compartments,  each  connected  by  an  individual  pipe  and 
valve  with  the  main  air-pipe  F.  By  this  means  the  air-pressure  to 
each  compartment  can  be  regulated  (by  throttling  the  valve)  to 
correspond  with  the  varying  hydraulic  head  within  the  tank,  so 
as  to  discharge  a  uniform  amount  of  air  throughout  the  length  of 
the  bottom  and  maintain  a  uniform  aeration  of  the  contents.  A 
pressure  of  from  4  to  5  Ib.  is  generally  used  and  each  square  foot 
of  porous  medium  requires  from  8  to  10  cubic  feet  of  free  air  per 
minute. 

Each  longitudinal  edge  of  the  tank  is  provided  with  a  lip  and 
an  overflow  gutter  for  the  reception  of  the  froth  to  be  discharged. 
The  lower  end  of  the  tank  is  furnished  with  a  spigot-discharge 


236 


THE   FLOTATION   PROCESS 


FIG.  44. 

fitted  with  a  plug-valve,  operated  by  a  float,  for  the  purpose  of 
maintaining  a  uniform  water-level  within  the  tank,  thus  in  turn 
securing  a  uniform  and  constant  discharge  of  froth  under  all  the 
varying  conditions  of  feed  incident  to  practical  milling  operations. 
The  water-level  may,  of  course,  be  varied ;  but  it  is  usually  maintained 


NOTES   ON   FLOTATION  237 

at  about  10  to  12  inches  below  the  level  of  the  overflow-lips.  The 
tailing  is  discharged  through  the  spigot  and  the  frothy  concentrate  is 
conveyed  by  means  of  the  side-gutters  to  the  pump  D-l,  thence  to 
the  cleaner-separatory  cells  marked  C.  This  cleaner-cell  is  a  machine 
of  the  same  construction  as  the  rougher;  in  operation,  however,  it 
is  usually  run  with  a  lower  air-pressure ;  the  tailing  from  the  cleaner 
is  pumped  by  Z>-2  back  to  the  original  feed,  and  thus  a  closed  circuit 
is  maintained  on  this  portion  of  the  feed.  The  concentrate  from  the 
cleaner  is  the  shipping  or  finished  product.  Dump  D-l  can  well  be 
eliminated  by  setting  the  cleaner  at  a  lower  elevation  and  conveying 
the  rougher-froth  to  it  by  gravity.  Usually  one  cleaner  serves  four 
roughers. 

PARALLEL  OR  SERIES.  The  machine  may  be  run  either  in  parallel 
or  in  series  without  any  sacrifice  in  capacity  for  a  given  number 
of  cells.  Recent  experience  goes  to  show  that,  on  some  ores  at  least, 
the  series  treatment  gives  a  slightly  better  tailing;  on  others  it  does 
not.  It  is  unnecessary  to  extend  this  arrangement  of  cells  beyond 
two  cells  in  series.  In  a  heavily  mineralized  ore  this  arrangement 
is  decidedly  advantageous  and  in  such  a  case  the  rougher-concentrate 
might  be  of  high  enough  grade  to  omit  the  re-cleaning  operation. 
The  froth  from  the  second  cell  in  the  series  might  be  returned  into 
the  original  feed  in  the  same  way  that  the  tailing  is  returned  from 
the  cleaner  when  practising  a  roughing  and  cleaning  operation.  A 
number  of  such  combinations  is  possible.  At  the  Inspiration,  the 
original  feed  goes  to  12  primary  roughers,  the  tailings  from  which 
are  classified  into  sand  and  slime,  the  sand  going  to  tables  and  the 
slime  being  returned  to  12  secondary  roughers.  The  concentrates 
from  both  the  primary  and  secondary  roughers  go  to  four  cleaners, 
and  the  cleaner-tailing  back  into  circuit. 

FROTH  FORMATION.  The  froth  is  generated  as  the  result  of 
injecting  the  finely  divided  air  into  the  bottom  of  the  already 
emulsified  pulp;  it  continues  to  form  and  to  overflow  so  long  as 
it  is  furnished  with  pulp  of  the  proper  consistence,  properly  mixed 
with  the  right  quantity  and  kind  of  oil  or  frothing  agent.  Measured 
from  the  water-level  within  the  tank,  the  froth  produced  may  be 
from  14  to  16  inches  in  depth  or  thickness,  and  according  to  the 
character  of  ore,  kind  and  quantity  of  oil  introduced,  will  be  more 
or  less  voluminous,  coarse  or  fine  grained,  dry  or  watery — all  of  these 
conditions  being  adjusted  by  the  regulation  of  the  kind  or  quantity 
of  oil  and  the  quantity  of  air  injected. 

In  the  case  of  some  ores,  rich  in  sulphides,  when  a  comparatively 


238 


THE   FLOTATION   PROCESS 


Teed  •  'OO  Tons  from  last  J  Spioota 
Ouerfoto  of  N*  1  Ctasaif>er. 

Scree*  Analysis  •    *  48  flea 
*6S 
+  100 
f/SO 


-too 


x.  7-ff- 

%% 

2  3.  If. 

ts.&< 

fSjf. 


-~f~LOT/1T/0/V 


-&- 

— DALY-  JUDGE  MILL. — 

TEST  N3  34. 


feed  by   Products  •    i»ad,  4.3S    Zinc,  /O.I4    Silver,   tO.CS 

-  Heads  Assay-      .,       4.9O        .       10.80       -          3.90      lrcn-4,5 


•W  GCHCWL  CNG/HCCHING  CO 
CONSUL  TIHG 

CtTYt    UTAH. 


Note.       fJ.Zji.of  Tot  at  Stiver 
48.ok4  !        . 
9S.SS%     .  • 


G.-J  Sit 


Contained  in  Lead  Concta. 


Lead  '  t.3fiicf  Tbtat  Leon. 
*  9.3ZJ*  .  .  Zinc. 
.  *///•  »  ••  Stfver. 


Lead  a  net  Zinc  Coxeta. 

than  OK  Stiver  in 


Siluer  ui  ZIKC  Conctz.  a  proeaely  carried  tu  trie  Copper,  and  is  loorth  1 5  cents  per 
tte    Lead  Concentrates. 
Actual  Sampling   Period  •  /£  Aeaas    running    on  'Ory' Ore. 

Time  Samples   tonen  witn  Stop  Watch   every  t  hour  on  feed,  Lead  Carets,  Zinc  Carets,  N:6 Tatle  Concts,  N'Z 
Cleaner  Concts,    and  General  fills,  for  S,  30,  IS,  30, 3O,  and  S  seconds   respectively.  . 

Oil  used  an  Orioinal  Fred  «  40 'f.  Coal  Tar,  40%  Cool  Tar  Creosote,  SOJ.  Pine  Oil  N*  6,  at  the  rate  of  0.6'es  per  Tarti.?) 
Oil  used  on  Zinc  Mids.fro*  N'6  Tatle  -9S%  Pine  Oil  N*6  and  S"f.  Coal  Tar  at  the  rate  of  t.5  tea.  p»r  Ten 
SO'  Slide  f^ute  Calculations. 


FIG  45. 


low-grade  concentrate  will  suffice,  the  'cleaner'  may  not  be  necessary, 

but  on  low-grade  ores  having  a  high  ratio  of   concentration   and 

demanding  a  concentrate  of  maximum  purity,  a  cleaner  is  desirable. 

PULP-DENSITY.    The  pulp  to  be  treated  may  be  of  varying  density, 


NOTES   ON   FLOTATION  239 

from  2J :  1  water  and  ore,  up  to  5  or  6:1;  for  a  mixture  of  sand 
and  slime  the  former  ratio  is  preferable,  but  for  a  pure  slime 
mixture  ( — 200-mesh)  the  larger  proportion  of  water  is  allowable. 
The  particular  density  is  not  a  matter  of  so  much  importance  as 
that  the  supply  of  pulp  be  uniform  in  density,  since  each  variation 
in  the  density  of  the  pulp  requires  a  re-adjustment  of  the  oil-supply, 
the  quantity  of  oil  increasing  in  proportion  to  the  increased  volume 
of  pulp,  independent  of  its  solid  content. 

CAPACITIES.  A  normal  capacity  per  standard  roughing-cell  is 
50  tons  per  24  hours.  This,  of  course,  will  vary  with  the  nature  of 
the  ore.  In  one  plant  that  employs  gravitation  previous  to  flotation 
the  fine  sand  and  slime  only  are  treated  at  the  rate  of  50  tons  per 
rougher.  The  Inspiration  Copper  Co.  uses  flotation  as  the  prime 
process,  and  its  800  tons  per  section  is  treated  by  24  roughing-cells 
and  4  cleaners.  In  this  case  the  cells  are  run  in  series,  the  primary 
cells  treating  the  original  feed  and  the  secondary  cells  re-treating 
only  the  slime  from  the  primary  tailing  after  the  sand  has  been 
removed.  This  gives  an  average  of  33.3  tons  per  roughing-cell.  The 
Arizona  Copper  Co.'s  plant  will  treat  the  slime  and  re-crushed  sand 
from  previous  gravity-treatment;  out  of  an  original  tonnage  of  4000 
there  will  be  about  3600  tons  of  flotation  feed.  This  will  be  handled 
on  63  roughers  run  in  parallel,  and  18  cleaners,  or  an  average  of 
approximately  57  tons  per  roughing-cell,  or  45  tons  per  cell  for 
roughing  and  cleaning. 

Some  tests  have  shown  little  difference  in  recovery,  whether 
running  45  tons  to  the  cell  or  65;  but  the  recoveries  commence  to 
decline  as  soon  as  the  feed  exceeds  75  tons.  In  the  Coeur  d'Alene, 
on  zinc-lead  ore,  35  tons  per  cell  is  an  average  capacity. 

OILS.  The  oils  used  may  be  broadly  divided  into  brothers'  and 
'  collectors. '  The  pine-oils  are  good  f rothers ;  coal-tar  and  its  various 
subdivisions  are  good  collectors.  On  some  ores  crude  pine-tar  will 
in  itself  combine  both  the  properties  of  frothing  and  collecting.  On 
others,  this  may  have  to  be  enriched  by  the  addition  of  some  one 
of  its  more  volatile  constituents,  such  as  refined  pine-oil,  turpentine, 
or  wood-creosote. 

Generally  speaking,  the  coal-tar  products  are  poor  frothers ;  to 
get  a  sufficient  volume  of  froth  to  insure  a  high  recovery,  it  is  often 
necessary  to  add  refined  or  crude  pine-oil,  creosote,  etc.  At  the 
Inspiration,  for  instance,  the  mixture  is  80%  crude  coal-tar,  20% 
coal-tar  creosote;  at  another  plant  on  similar  ore  45%  El  Paso 
coal-tar,  40%  coal-tar  creosote,  10%  cresol,  and  5%  pine-oil.  At 


240 


THE   FLOTATION    PROCESS 


the  Daly- Judge  we  used  40%  crude  coal-tar,  40%  creosote,  20% 
pine-oil.  In  the  Coeur  d'Alene  on  zinc  ore  we  used  straight  wood- 
creosote;  on  the  National  Copper  ore  plain  turpentine  will  work. 


but  pine-oil  is  better.  At  the  Inspiration  we  used  from  1£  to  2 
pounds  of  the  mixture  per  ton  of  ore ;  at  the  Daly- Judge,  1  to  1J  Ib. ; 
and  at  the  National  0.3  Ib.  oil  is  sufficient.  In  the  experimental  work 
at  another  plant  the  consumption  of  oil  was  approximately  one  pound 


NOTES   ON    FLOTATION  241 

of  mixture  per  ton,  but  since  the  entire  plant  has  been  in  operation 
and  the  circuit-water  is  reclaimed  and  used  over  again,  the  oil 
consumption  has  dropped  from  1  to  0.35  Ib.  The  proper  kind  or 
kinds  of  oil  and  the  quantity  requisite  can  only  be  determined  at 
present  by  tentative  experiment;  so  far  no  scientific  short-cut  is 
known. 

CHARACTER  OF  FROTH.  The  nature  of  the  froth  made  by  the 
pneumatic  method  has  the  distinctive  characteristic  of  being  unstable 
or  ephemeral,  that  is,  it  quickly  dies  when  removed  from  the  action 
of  the  injected  air.  The  bubbles  composing  the  froth,  being  generated 
under  a  hydraulic  pressure  varying  from  15  to  40  inches,  on  rising 
above  the  water  and  to  the  froth-level,  burst  by  reason  of  the  lower 
surrounding  atmospheric  pressure.  On  bursting,  they  release  the 
mineral  attached  to  them,  but  this  in  turn  is  caught  up  by  those 
bubbles  immediately  following  behind.  The  instability  or  stability 
of  the  bubbles  will  depend,  to  some  extent,  upon  the  oil  used  and 
the  nature  of  the  gangue.  Pine-oil  makes  a  very  brittle  froth,  which 
dies  immediately  on  arriving  at  the  surface.  Creosote  and  light  oil 
make  a  more  elastic  envelope,  which  at  times  will  expand  into  bubbles 
3  to  4  inches  in  diameter  before  bursting.  The  pine-oil  bubbles 
will  rarely  be  over  J  or  \  inch  diameter.  Castor-oil,  olive-oil,  candle- 
makers*  oil  (oleic  acid),  palm-oil,  sperm-oil,  and  other  oils  of  a 
lubricating  nature,  have  in  general  been  replaced  by  oils  more 
or  less  soluble  or  miscible  in  water — such  as  turpentine,  pine-oil,  and 
all  the  coal  and  wood-tar  distillations.  The  very  volatile  oils,  such 
as  naphtha,  gasoline,  ether,  alcohol,  seem  to  serve  very  little  purpose 
except  as  a  means  for  making  the  pitchy  ingredients  of  the  tars  more 
soluble  or  miscible. 

A  large,  coarse,  and  elastic  bubble  seems  necessary  to  the  recovery 
of  coarse-grained  mineral,  but  for  the  very  fine  or  colloidal  mineral, 
a  small  and  comparatively  brittle  bubble  is  necessary. 

POWER.  The  National  Copper  Co.,  using  approximately  950 
cubic  feet  of  air  at  4-lb.  pressure,  and  treating  500  tons  per  day  on 
8  roughers  and  2  cleaners,  required  35-hp. ;  this  equals  3.5  hp.  per 
cell,  or  12.53  tons  per  horse-power,  or  1.25  kw.-hours  per  ton. 

Another  company  using  approximately  9600  cubic  feet  of  air 
at  5-lb.  pressure  and  treating  2400  tons  per  day  on  48  roughers 
and  12  cleaners,  required  210  hp. ;  this  equals  3.5  ^p.  per  cell,  or 
11.45  tons  per  horse-power,  or  1.56  kw.-hours  per  ton. 

The  Inspiration  experimental  plant,  using  approximately  950 
cu.  ft.  of  air  at  5-lb.  pressure  and  treating  200  tons  per  day  with 


242 


THE   FLOTATION    PROCESS 


u 


^^^^^^^^^^^^^^^^ 

sWir 


NOTES   ON    FLOTATION 


243 


4  roughers  and  1  half-size  cleaner  required  25  hp. ;  deducting  4  hp. 
for  two  2-in.  centrifugal  pumps,  this  equals  20  hp.,  or  4  hp.  per  cell, 
or  10  tons  per  horse-power,  or  1.79  kw.-hours  per  ton. 


A  maximum  figure  would  be  2J  kw.-hours  per  ton  of  feed,  using 
5  to  5J-lb.  air-pressure,  generated  by  a  Roots  or  Connersville  positive 
blower. 


244  THE  FLOTATION  PROCESS 

COST.  The  oil-mixtures  generally  in  use  will  cost  from  1.25c.  up 
to  3c.  per  Ib.  depending  on  the  proportion  of  cresol  and  other  high- 
priced  oils  used,  but  IJc.  per  Ib.  will  be  a  safe  average  on  most 
oils.  A  consumption  of  1  to  1J  Ib.  per  ton  or  from  1.25c.  to  4.5c. 
per  ton  of  feed,  say  2|c.,  would  be  a  safe  average.  The  labor, 
of  course,  will  vary  with  the  size  of  the  plant.  At  one  plant 
consisting  of  60  cells,  two  men  per  shift  operate  the  entire  plant, 
equivalent  to  a  cost  of  IJc.  per  ton.  One  man  per  shift  on  a  250-ton 
plant  will  mean  a  cost  of  5.4c.  per  ton  in  maintenance.  Assuming 
a  life  of  three  months  per  blanket  and  50  tons  per  cell  and  an 
allowance  for  repairs  to  blowers,  motors,  pumps,  etc.,  we  have  £c. 
per  ton  as  a  liberal  estimate. 

Power  at  Ic.  per  kw.hour  ($60  per  hp.-year)  and  2J  kw.-hours 
per  ton  equals  2.5c.  per  ton  of  feed. 

Summarized,  my  estimate  on  a  2000-ton  plant  will  stand  approxi- 
mately as  follows,  in  cents  per  ton  of  feed : 

Labor    1.25 

Oil 2.50 

Maintenance    0.50 

Power   2.50 

Total 6.75 

On  a  plant  of  250  tons  the  extra  labor  would  bring  it  up  to 
approximately  lOc.  per  ton.  Actual  figures  from  a  large  plant  of 
over  2000  tons  grave  6.1c.  per  ton.  The  flotation  feed  in  this  case 
represents  60%  of  the  crude-ore  tonnage  or  3.5c.  per  ton  of  crude 
ore  treated. 

THEORIES.  So  far  no  satisfactory  explanation  of  flotation  phe- 
nomena has  been  advanced.  At  my  instigation  and  under  my  direction, 
a  large  amount  of  research  work  has  been  done  in  an  earnest  endeavor 
to  formulate  some  logical  explanation,  and  perhaps  to  find  some 
scientific  way  of  conducting  experiments  in  lieu  of  the  empirical 
methods  now  in  vogue.  While  this  purpose  has  not  yet  been  fully 
attained,  the  experiments  have  resulted  in  the  formulation  of  a 
theory  that  appears  to  be  well  grounded  and  that  may  prove  of 
value  to  others  engaged  in  this  branch  of  metallurgy. 

Much  work  has  been  done  at  the  Mellen  Institute  at  Pittsburg 
under  the  direction  of  Raymond  C.  Bacon,  and  lately  by  James  A. 
Block  at  the  local  station  of  the  U.  S.  Bureau  of  Mines.  The  results 
of  some  of  this  work  are  summarized  in  the  following  statements: 


NOTES   ON    FLOTATION  245 

In  considering  the  connection  between  flotation  phenomena  and 
the  physical  properties  of  the  minerals  concerned,  there  are  two 
parallelisms  to  be  noticed : 

First :  It  has  been  noticed  for  some  time  that  the  minerals  which 
floated  were  not  easily  wetted  by  water,  while  those  which  were 
easily  wetted  did  not  tend  to  come  up  with  the  froth.  This  is  the 
basis  of  about  the  only  theory  that  has  been  widely  circulated  up 
to  this  time.  It  is  well  stated  by  Hoover  in  his  book,  '  Concentrating 
Ores  by  Flotation,'  the  first  authoritative  publication  on  the  subject. 

Second:  There  is  a  parallelism  between  certain  electro-static 
characteristics  and  the  flotation  properties  of  ores,  as  will  be  explained. 

In  the  theory  first  mentioned,  it  may  be  demonstrated  by  a 
consideration  of  surface  tensions  and  contact  angles  that  certain 
floatable  minerals,  such  as  galena,  will  float  on  the  surface  of  still 
water,  while  gangue  particles,  on  the  other  hand,  possess  a  greater 
adhesive  attraction  for  the  water  than  the  water's  cohesive  attraction 
for  itself,  and  are  therefore  drawn  through  the  surface  film  into 
the  interior,  where  they  sink  because  of  their  greater  specific  gravity. 
These  properties  of  floatable  minerals  and  gangues  are  increased 
by  the  presence  of  oil  and  acid.  Oil  sticks  to  galena  with  greater 
tenacity  than  it  sticks  to  silica,  and  an  oil  surface  is  far  less  easily 
wetted  than  a  galena  surface.  The  acid  in  the  water  causes  a  still 
greater  difference  in  the  various  surface  tensions.  This,  it  seems, 
is  without  question  the  explanation  of  such  flotation  as  is  obtained 
by  the  Macquisten  process,  in  which  the  ore  particles  are  lifted  to 
the  surface  and  those  remaining  are  removed  by  skimming  the  surface 
layer  of  the  liquid. 

As  regards  the  second  parallelism  mentioned,  it  has  been  noticed 
that  extremely  small  amounts  of  certain  colloidal  impurities,  such 
as  saponine  or  tannine,  were  detrimental  to  flotation,  while  others, 
such  as  Congo  red  and  methyline  blue,  did  not  interfere,  and  were, 
if  anything,  beneficial.  In  classifying  these,  the  injurious  ones 
generally  came  under  the  head  of  what  physical  chemists  call  electro- 
negative colloids,  while  electro-positive  colloids  were  not  harmful. 
This  classification  is  derived  from  the  fact  that  suspended  particles 
will  generally  migrate  when  placed  in  an  electric  field,  and  the 
classification  comes  naturally  from  the  direction  of  their  migration. 
This  migration  is  called  electro-phoresis,  or  electrical  endosmose,  and 
is  the  result  of  the  fact  that  the  liquid  containing  the  particles  forms 
contact-layers  around  them,  similar  to  the  surface-films  formed 
when  liquids  come  in  contact  with  air.  These  contact-films  almost 


246  THE  FLOTATION  PROCESS 

invariably  have  a  difference  of  potential  between  their  inner  and 
outer  surfaces.  The  film  of  an  air-water  contact  has,  for  instance, 
a  difference  of  0.055  volts,1  and  other  contact-films  have  similar 
charges.  This  causes  the  particles  to  act  like  charged  solids,  and 
to  be  attracted  by  electric  charges  of  opposite  sign. 

The  charges  on  solids  and  non-miscible  liquids  can  be  conveniently 
studied  on  the  stage  of  a  microscope. 

This  work  led  naturally  to  the  study  of  the  charges  exhibited 
by  various  ores  and  minerals,  and  in  that  work  an  interesting 
parallelism  was  observed;  namely,  that  floatable  minerals  seemed  to 
have  positive  charges  and  non-floatable  gangues  negative  charges.2 
Some  gangues  were  found  with  positive  charges,  but  they  were 
characteristically  hard  to  handle,  having  a  tendency  to  come  up 
with  the  froth.  These  charges  sometimes  vary  with  the  acidity  or 
alkalinity  of  the  liquid,  and  this  variation  is  not  inconsistent  with 
the  effects  of  acidity  or  alkalinity  on  the  flotation  of  ores. 

It  has  been  noticed  that  these  electro-static  properties  depend  on 
the  condition  of  the  surface  of  the  particles  and  not  upon  the 
composition  of  the  mass.  For  instance,  lead  oxide,  which  is  ordinarily 
negative  or  neutral,  when  covered  with  a  sulphide  coating  takes  upon 
itself  a  positive  charge. 

Although  these  charges  are  small,  recent  work  on  the  coagulation 
and  deflocculation  of  slime,  on  the  coagulation  and  dispersion  of 
colloids,  and  along  similar  lines,  shows  that  the  contact-film  charges 
have  an  important  bearing  on  the  dispersion  or  coherence  of  particles 
suspended  in  liquid  mediums.  In  fine  suspensions  and  in  colloidal 
solutions,  these  charges  may  often  be  neutralized  by  the  introduction 
of  oppositely-charged  ions,  and  precipitation  will  generally  take  place 
whenever  these  charges  fall  below  certain  limits.  Oppositively- 
charged  contact-films  generally  have  a  tendency  to  absorb  each  other, 
and  to  coalesce,  while  similarly-charged  films,  if  their  charges  are 
great  enough  to  overcome  natural  cohesiveness,  do  not  seem  to  coalesce, 
but  to  repel  each  other,  and  if  the  weight  of  the  particles  is  small 
enough  in  relation  to  their  size  and  surface,  permanent  dispersion 
will  take  place,  the  particles  distributing  themselves  through  a  liquid 
in  much  the  same  manner  that  a  gas  will  fill  a  container. 

In  view  of  the  above  observations,  it  seems  possible  that  flotation 
is  due  to  differences  in  polarity  in  the  charges  on  the  various  particles 


^Philosophical  Magazine,  1914,  27:  297  and  28:  367. 

^Kolloid    Chemische    Beihefte,    2:84;     Zeit.    filr    Physikalische    Chemie, 
89:  91,  1914. 


NOTES   ON    FLOTATION  247 

of  ore,  and  on  the  bubbles.  Since  oil  contact-films  and  air  contact- 
films  have  both  been  proved  to  have  negative  charges,  the  positively- 
charged  minerals  might  adhere  to  either.  The  bubble-mantles  in  a 
flotation  machine  are  undoubtedly  composed  of  oil,  or  of  oil  in 
emulsion,  since  pure  water  alone  will  not  froth.  The  same  forces, 
then,  that  cause  oppositively-charged  colloids  to  agglomerate  and 
precipitate,  cause  the  minerals  to  adhere  to  the  oil-covered  bubbles; 
and  the  same  forces  that  keep  the  particles  of  an  oil  emulsion 
dispersed,  keep  the  gangue-particles  repelled  from  the  bubbles. 

Expressed  briefly,  the  theory  is  as  follows:  That  oil  flotation  is 
an  electro-static  process.  It  is  a  scientific  fact  that  when  a  solid 
particle  is  suspended  in  water,  the  water  will  form  around  the 
particle  a  contact-film  that  generally  possesses  an  electric  charge, 
the  amount  and  polarity  of  which  will  depend  upon  the  nature  of 
the  surface  of  the  particle  and  the  electrolyte  in  which  it  is 
suspended.  The  presence  of  these  charges  can  be  demonstrated  by 
the  fact  that  the  particles  possessing  them  will  migrate  when  placed 
in  an  electric  field.  It  has  been  demonstrated  that  floatable  particles 
have  charges  of  one  polarity  (positive),  and  that  non-floatable 
particles  have  charges  of  the  opposite  polarity  (negative),  and  that 
the  froth  is  charged  negatively  and  so  attracts  the  positively-charged 
or  floatable  minerals,  and  repels  the  negatively-charged  or  non- 
floatable  ones.  It  is  this,  it  is  believed,  that  causes  the  floatable 
minerals,  such  as  galena  or  sphalerite,  to  adhere  to  the  froth  and 
rise,  while  the  gangue-minerals,  such  as  silica  and  limestone,  remain 
in  the  liquid  where  they  can  be  discharged  as  tailing. 


248  THE  FLOTATION  PROCESS 

DISPOSAL   OF   FLOTATION   RESIDUE 

By  W.  SHELLSHEAR 
(From  the  Mining  and  Scientific  Press  of  December  11,  1915) 

*!NTRODUCTION.  There  are  many  methods  of  handling  sand  and 
slime  from  metallurgical  operations,  but  in  this  article  the  draining 
and  conveying  of  waste  products  from  flotation  processes  will  be 
specially  dealt  with,  the  methods  given  being  those  in  use  at  the 
leading  flotation  plants  in  Australia. 

DRAINING  AND  DEWATERING.  It  is  generally  advisable  to  thor- 
oughly dewater  the  residue  from  flotation  treatment  in  order  to 
form  a  closed  circuit  of  liquor.  This  maintains  constant  conditions 
throughout  the  plant  and  avoids  waste  of  oil,  which  would  be  carried 
away  by  the  solution  with  the  tailing.  The  methods  that  may  be 
used  for  this  purpose  are : 

(a)  Filtering  in  vats;  (b)  combination  of  a  submerged  draining- 
belt  and  Dorr  thickeners;  (c)  combination  of  Caldecott  diaphragm- 
cones,  draining-belt,  and  Dorr  thickeners,  and  (d)  combination  of 
Dorr  classifiers  and  Dorr  thickeners. 

FILTERING  IN  VATS.  In  this  system,  shown  in  Fig.  50,  the  pulp 
from  flotation  is  run  direct  into  vats.  These  are  usually  15  ft.  diam., 
their  depth  varying  from  10  to  20  ft.  In  the  centre  of  each,  and 
before  filling,  a  tube  or  pipe,  15  in.  diam.,  that  fits  over  the  circular 
discharge-hole,  is  inserted.  When  the  vat  is  ready  for  emptying, 
this  tube  is  lifted  out,  a  large  proportion  of  the  tailing  falling 
through  the  centre  hole  onto  a  conveyor  underneath.  The  remainder 
is  afterward  shoveled  upon  the  same  conveyor. 

A  wooden  frame,  not  shown  in  the  sketch,  is  erected  above  the 
vat  to  support  the  lifting-device,  a  screw-block  being  used  to  raise 
the  pipe  to  the  desired  height.  This  operation  is  afterward  carried 
out  by  an  ordinary  block  and  tackle.  The  vat  may  be  made  of  wood 
or  iron,  and  the  height  to  which  it  may  be  constructed  is  controlled 
by  local  conditions,  such  as  the  design  of  the  plant,  and  the  nature 
and  fineness  of  the  material  to  be  filtered.  It  is,  however,  apparent 
that  the  greater  the  height  that  can  be  economically  employed,  the 
less  the  labor  required,  as  a  proportionately  large  amount  drops 
through  the  centre  of  the  vat  without  shoveling.  This  would  tend 
to  make  the  inner  tube  too  long  to  be  handled  conveniently,  but  the 


•Abstract  from  Min.  and  Eng.  Review,  Melbourne,  Australia. 


DISPOSAL    OF    FLOTATION    RESIDUE 


249 


difficulty  has  been  overcome  by  making  the  tube  in  sections,  each 
of  which  is  lifted  in  its  turn  from  the  top  as  emptying  proceeds. 

The  time  of  filtering  is  arranged  according  to  the  number  of 
vats  employed,  but  it  is  the  usual  practice  to  run  the  pulp  through 


FIG.   49.      AUSTBALIAN  BOOM-DISTBIBUTOB.      BELT-DBIVEN   WITHOUT   GEAR  AT   900  FT. 

PEB  MIN.  BY  SLOW-SPEED  MOTOB  CONTROLLED  FBOM  BELOW.      THE  MACHINE 

CAN    BE   MOVED    WHILE   WOBKING. 

a  number  in  series,  so  that  the  slime  settles  from  the  solution. 
Thus,  if  six  vats  are  in  use,  one  may  be  draining  and  another 
emptying,  while  the  remainder  would  be  used  for  the  pulp  flowing, 
in  series,  through  them.  The  filtered  water  is  carried  off  by  a 


250  THE  FLOTATION  PROCESS 

number  of  pipes  at  the  bottom  of  each  vat.  Under  certain  conditions 
a  suction-pump  is  connected  to  these  pipes  to  assist  the  filtering,  but 
this  is  not  the  usual  practice.  As  a  filtering  medium,  cocoa-nut 
matting  is  used  generally. 

After  a  vat  has  been  emptied,  the  tube  is  dropped  into  the 
discharge-hole,  two  lugs,  one  on  each  side  keeping  it  in  position. 
The  open  space  round  the  tube  is  then  filled  with  clay.  It  is 
advisable  to  have  the  bottom  of  the  vat  six  feet  above  the  ground- 
level  to  allow  of  easy  access  to  the  conveyor  underneath.  At  the 
spot  where  the  sand  is  discharged  upon  the  conveyor-belt,  guide- 
doors  are  arranged  parallel  with  the  belt  to  prevent  sand  going  over 
its  edge,  and  the  number  of  idlers  under  the  conveyor  is  increased 
to  prevent  it  sagging  under  a  rush  of  feed.  The  conveyor  is  usually 
a  flat  belt,  24  in.  wide,  traveling  at  350  to  450  ft.  per  minute, 
4-in.  iron  idlers  being  used. 

This  method  has  many  excellent  features;  its  advantages  are: 
(1)  The  moisture  of  the  drained  tailing  is  less  than  in  any  other 
system;  (2)  the  slime  is  drained  at  the  same  time  as  the  sand; 
(3)  dams  for  handling  the  slime  and  the  cost  of  labor  on  same  are 
eliminated;  (4)  dusting  troubles  are  minimized  on  the  dump,  owing 
to  the  slime  helping  to  set  the  tailing;  (5)  the  angle  of  repose  of 
the  dump  is  increased,  thus  enabling  more  sand  to  be  stacked  per 
unit  of  ground-area;  (6)  no  trouble  with  conveyors  handling  tailing 
will  cause  a  stoppage  in  the  main  plant;  (7)  accurate  sampling  of 
products  is  possible,  enabling  shift-work  to  be  kept  under  control. 

The  disadvantages  are:  (1)  High  initial  cost  of  erection;  (2) 
relatively  high  cost  of  labor  in  emptying  vats;  (3)  clarification  of 
solution  is  not  usually  as  complete  as  is  the  case  with  other  methods. 

COMBINATION  OP  DRAINAGE-BELT  AND  THICKENERS.  The  idea  of 
the  submerged  draining-belt,  I  think,  was  first  introduced  in  connec- 
tion with  the  Elmore  process  in  order  to  overcome  the  difficulty  of 
discharging  the  residual  pulp  without  upsetting  the  vacuum  in  the 
flotation  apparatus.  In  this  system  the  belt  runs  inside  an  iron 
trough  filled  with  water,  being  forced  into  a  semi-circular  shape 
by  means  of  a  spherical  pulley,  as  shown  in  sketch,  Fig.  51.  The 
belt  travels  under  water  for  a  certain  distance,  rising  at  a  slope 
of  15  to  20°  onto  the  head  pulley. 

The  drive  is  usually  from  the  tail-end  by  means  of  a  worm- 
wheel  on  the  tail-pulley  shafting.  This  tail-pulley  is  generally 
6  ft.  diam.,  and  is  faced  on  the  outside  with  wooden  boards  to  give 
the  belt  a  better  grip.  The  feed  is,  preferably,-  distributed  to  the 


DISPOSAL   OF    FLOTATION   RESIDUE 


251 


belt  by  means  of  an  iron  launder  with  holes  in  the  bottom,  wooden 
guides  being  arranged  to  guard  against  sand  getting  between  the 
under  side  of  the  belt  and  the  trough.  The  trough  has  side  launders 
attached  to  carry  the  overflow  to  Dorr  thickeners,  the  number  of 


ID 

in 


]\ 


i 


the  latter  depending  on  general  conditions,  such  as  nature  of  slime, 
amount  of  water  in  circulation,  etc.  The  submerged  belt  forms  an 
excellent  desliming  system,  by  reason  of  the  classification  in  the 
trough ;  its  capacity  is  4000  or  more  tons  a  week  of  mixed  slime  and 


252 


THE   FLOTATION    PROCESS 


sand.    The  draining  of  the  sand  is  accomplished  as  it  rises  from  the 
surface  of  the  liquid  in  the  trough  to  the  head  pulley. 


In  order  to  accelerate  this  draining  action,  a  bumper  is  usually 
employed.  This  consists  of  an  idler  driven  by  two  eccentrics.  The 
vibration  caused  on  the  belt  by  the  idler  striking  it  underneath 


DISPOSAL   OF    FLOTATION    RESIDUE  253 

displaces  a  larger  quantity  of  water  from  the  sand,  and  thus  reduces 
the  proportion  of  moisture  in  the  final  product.  An  iron  scraper  is 
used  for  removing  the  tailing  from  the  draining-belt ;  it  may  be 
kept  under  pressure  by  means  of  iron  springs.  This  method  is  very 
good,  especially  where  the  room  available  for  drainage  is  limited. 
It  is  also  convenient  where  the  height  of  the  flotation-plant  above 
the  ground  is  small. 

The  life  of  the  belt  is  less  than  that  of  an  ordinary  draining-belt, 
owing  to  the  heavy  pressure  of  the  spherical  roller,  and  the  action 
of  the  hot  circuit-liquors  in  which  the  belt  is  submerged.  The  labor 
for  attendance  is  small.  This  method  is  at  present  in  use  on  two 
of  the  large  flotation  plants  at  Broken  Hill. 

COMBINATION  OF  CONES,  DRAINING-BELT,  AND  THICKENERS.  This 
method,  diagrammatically  illustrated  in  Fig.  52,  has  been  installed 
in  the  latest  flotation-plant  at  Broken  Hill.  The  size  of  the  Caldecott 
cones  usually  employed  is  12  ft.  diam.  and  10  ft.  deep,  the  diaphragm 
being  2  ft.  to  2  ft.  6  in.  from  the  bottom  of  the  cone.  In  most  cases 
a  plate-diaphragm  is  used,  but  the  introduction  of  an  iron  ball  to 
serve  the  same  purpose  has  been  most  successful.  Where  a  cone  of 
this  type  is  used  as  a  thickener,  rather  than  as  a  slime-classifier, 
more  pulp  may  be  thickened,  as  the  height  of  pulp  need  not  be 
so  finely  adjusted.  Still,  it  is  customary  to  keep  the  level  of  the 
sand  two  feet  from  the  top  of  the  cone,  as  measured  in  the  centre. 
The  feed  usually  passes  into  these  cones  through  a  centre  of  the 
Callow  type. 

To  remove  the  thickened  pulp  continuously  and  divert  it  onto 
the  draining-belt,  an  ordinary  plug  may  be  used  with  advantage, 
provided  coarse  rubbish  has  been  removed  previously.  Another 
successful  device  is  a  plug-valve  or  a  plug  worked  from  the  top, 
fitting  into  a  seat  at  the  bottom  of  the  cone.  The  type  of  draining- 
belt  employed  is  36  in.  wide.  The  belt  rises  gradually,  about  1  in  60, 
from  the  tail-pulley,  the  last  30  ft.  of  the  slope  being  increased  to 
about  20°.  The  belt-speed  is  20  to  30  ft.  per  min.,  both  ordinary 
and  troughing  idlers,  of  6-in.  diam.,  being  used.  As  the  operation 
of  the  belt  is  slow,  wooden  idlers  working  in  cast-iron  'dead-eyes' 
can  be  successfully  used  for  the  horizontal  idlers,  the  troughing- 
idlers  being  of  the  usual  type. 

The  drive  is  at  the  head  end,  double  gearing  for  speed  reduction 
being  employed.  The  head-pulley  is  generally  5  ft.  diam.,  the  snub- 
pulley  18  in.  diam.,  and  arc  of  contact  200  to  250°.  The  tail-pulley 
is  usually  2  ft.  diam.  Rubber  belting  on  the  face  of  these  pulleys 


254 


THE   FLOTATION    PROCESS 


reduces  the   slip,   thereby   increasing   the   power-efficiency   and   the 
life  of  the  belt. 

The  overflow  from  the  Caldecott  cones  goes  into  one  or  more 
Dorr  thickeners,  according  to  requirements,  the  underflow  from  the 
thickeners,  as  in  other  methods,  being  handled  with  flooded  suction- 


pumps.  Attempts  to  mix  the  underflow  from  the  Dorr  thickener 
with  pulp  on  the  draining-belt  in  order  to  convey  them  together  to 
the  pump  have  not  so  far  proved  successful.  For  the  control  of  the 
underflow  from  Dorr  thickeners  the  hydrometer  method  (described 
in  'Rand  Metallurgical  Practice')  has  proved  quite  satisfactory,  a 
constant  pulp,  with  Broken  Hill  slime  of  50%  solid  being  easily 


DISPOSAL    OF    FLOTATION    RESIDUE  255 

maintained.  This  method  is  considered  a  good  one,  because  the 
cost  of  labor  is  low,  the  life  of  the  draining-belt  is  prolonged,  and 
the  cost  of  maintenance  is  small.  Adequate  head-room  is,  however, 
necessary  for  the  erection  of  the  cones;  in  some  cases  elevation  is 
essential.  A  disadvantage  is  that  a  stoppage  of  the  dump-belts  causes 
a  stoppage  of  the  whole  plant. 

COMBINATION  OF  CLASSIFIERS  AND  THICKENERS.  This  method  has 
not,  to  my  knowledge,  yet  been  adopted  at  any  plant  in  Australia, 
but  the  great  success  that  it  has  achieved  at  cyanide  plants  in 
America  shows  that  it  could  be  applied  to  the  handling  of  tailing 
and  slime  products  at  Broken  Hill.  The  usual  type  of  Dorr  classifier, 
however,  would  have  to  be  especially  lengthened  to  cause  extra 
draining  of  the  sand  product.  Owing  to  the  regular  working  of 
these  machines  the  usual  draining-belt  may  be  discarded.  At  the 
same  time  very  little  head-room  would  be  required.  This  method 
is  illustrated  in  Fig.  53,  which  shows  the  classifiers  delivering  direct 
onto  the  inclined  belt.  It  has,  however,  the  same  disadvantage  as 
the  method  last  mentioned,  in  that  it  does  not  make  the  treatment- 
plant  independent  of  the  dump-belt  stoppages.  The  cost  of  erection 
and  maintenance  would,  however,  be  small. 

HANDLING  OF  DRAINED  PRODUCTS.  Tailing  may  be  handled  in  the 
following  ways:  (a)  Inclined  conveyor-belts  and  boom-stackers,  (b) 
aerial  trams,  (c)  trucking,  and  (d)  sluicing. 

INCLINED  CONVEYOR-BELTS  AND  BOOM-STACKERS.  The  usual  angle 
for  an  inclined  conveyor  is  20°  ;  where  possible  the  conveyor  should 
be  driven  from  the  head-end.  Where  the  head-end  is  high  above  the 
ground,  the  drive  should  be  either  from  the  tail-end  or  from  a  large 
centre-pulley,  midway  along  the  belt,  having  a  snub-pulley  at  each 
side  above  it,  the  centre-pulley  being  6  to  8  ft.  diam.  and  resting, 
preferably,  on  a  concrete  base. 

The  inclined  conveyor  is  first  of  all  built  on  trestles  at  the  angle 
required.  As  the  size  of  the  dump  increases,  the  conveyor  is 
extended  in  the  form  of  a  cantilever,  held  by  guy-ropes  from  the 
upright  trestles  in  the  dump.  A  belt  to  handle  40  to  50  tons  per 
hour  would  require  to  be  one  of  24  in.  six-ply  rubber  built  on  3  to 
10-in.  stringers,  placed  3-ft.  centres.  If  driven  from  the  head-end, 
the  driving  pulley  should  be  5  ft.  diam.  gear-driven,  the  tail-pulley 
being  2  ft.  diameter. 

The  Australian  practice  is  to  use  separate  rollers  and  troughing- 
idlers  instead  of  a  combination  idler.  This  practice  is  simple;  the 
idlers  can  be  more  easily  lubricated.  The  best  size  of  roller  is  4  in. 


256 


THE   FLOTATION    PROCESS 


diam.  It  is  usually  made  of  steel  pipe  shrunk  onto  cast-iron  end 
pieces.  A  favorite  practice  is  to  have  idlers  and  dead-eyes  on  the 
top  of  the  same  stringers,  the  loaded  and  return  belt  running  on 
rollers  supported  by  the  same,  and  being  about  three  inches  apart. 


The  top  rollers  are  usually  spaced  4  to  6  ft.  centres,  the  return  idlers 
being  spaced  at  twice  this  distance  apart.  Wooden  rollers  for  fast 
belts  of  this  type  are  not  satisfactory. 

In  calculating  the  power  required  for  this  type  of  belt  it  is  well 


DISPOSAL   OF   FLOTATION   RESIDUE  257 

to  remember  that  the  horsepower  lost  in  friction  per  100  ft.  varies 
inversely  as  the  length  of  the  belt,  averaging  from  2  to  6  hp.  per 
100  ft.  A  tightening  arrangement  is  usually  fixed  on  the  tail-pulley 
of  this  type  of  belt  to  cause  it  to  run  true  and  take  up  any  unneces- 
sary slack.  When  an  inclined  conveyor  has  been  carried  out  to  an 
economical  distance,  the  tailing  at  its  end  is  made  into  a  bed  for 
a  boom-stacker.  This  is  an  iron  pole,  which  is  held  in  position  by 
four  strong  guy-ropes.  Attached  to  the  pole  is  an  iron  lattice-girder, 
which  is  supported  similar  to  a  cantilever  by  guy-ropes  attached 
to  the  pole  itself.  This  boom-stacker  rests  on  a  steel  ball  in  a  cup- 
shaped  receiving  device,  which  enables  it  to  swing  around  as  desired. 
The  weight  of  the  boom-stacker  is  spread  over  a  large  area  by  means 
of  a  number  of  heavy  timbers  resting  in  the  prepared  foundation 
on  the  dump.  The  conveyor  on  the  boom-stacker  is  driven  by  a 
motor  fixed  behind  the  boom,  and  traveling  around  with  it.  [The 
photograph  (Fig.  49)  shows  a  good  boom-stacker  at  Kalgoorlie, 
Western  Australia,  from  which  place  the  Broken  Hill  system  was 
largely  copied. — EDITOR.] 

AERIAL  TRAMS.  These  are  so  well  known  that  they  need  no 
description  here.  For  moderate  tonnage  they  are  seldom  used,  as  a 
bin  is  required  and  two  men  loading  and  operating  trucks. 

HANDLING  OF  SLIME.  The  pulp  from  Dorr  thickeners  is  either 
transferred  by  flooded-suction  centrifugal  pumps  or  three-throw 
pumps,  or  else  elevated  by  an  ordinary  belt-elevator.  Where  there 
is  room  for  a  slime-dam  close  to  the  treatment-plant,  the  belt-elevator, 
which  is  a  very  economical  system  of  elevation,  may  be  used.  In 
other  cases  centrifugal  pumps  are  resorted  to.  The  thickened  pulp 
may  also  be  delivered  to  dams  or  sprayed  onto  the  surface  of  sand- 
dumps.  To  remove  the  drained  water  it  is  preferable  to  use  a  wooden 
box-launder.  This  consists  of  two  box-launders  connected  in  the 
form  of  a  right  angle,  and  fixed  in  position  at  the  starting  of 
the  building  of  the  dam.  The  horizontal  portion  of  the  launder 
is  laid  12  ft.  inside  the  dam,  and  is  carried  to  the  water-sump 
outside  it.  The  vertical  portion  passes  through  the  slime  and  is 
bored  with  holes,  which  are  plugged  from  the  bottom  upward  as 
the  building  of  the  dam  proceeds.  Probably  the  best  method  of 
handling  slime-pulp  is  to  pump  it  through  a  nozzle  onto  the  surface 
of  sand-dumps.  By  such  means  it  may  be  sprayed  evenly  all  over 
the  dump.  This  does  away  with  dams,  and  checks  the  dust  rising 
from  the  sand-dump.  The  idea  was  first  originated  in  South  Africa, 
and  has  only  lately  been  introduced  into  Australia. 


258  THE  FLOTATION  PROCESS 

THE  ELECTRICAL  THEORY  OF  FLOTATION—  II 

By  THOMAS  M.  BAINS,  JR. 
(From  the  Mining  and  Scientific  Press  of  December  11,  1915) 

The  article  in  the  Mining  and  Scientific  Press  of  October  23, 
1915,  by  Mr.  0.  C.  Ralston,  has  brought  out  many  points  of  interest. 
It  seems  to  me,  however,  that  the  fundamental  principles  of  flotation 
can  best  be  studied  with  larger  particles,  thus  avoiding  the  interesting, 
but  also  little  undestood  '  colloid  '  chemistry.  In  gravity  separation 


by  rising  currents  of  water,  Rittinger's  formula  V  =  cVD  (S-L) 
holds  true  for  particles  above  a  certain  size,  namely,  about  0.2  mm. 
for  quartz  and  0.13  mm.  in  case  of  galena.  Below  these  sizes, 
colloidal  and  other  little-known  phenomena  become  of  importance 
and  complicate  the  investigation.  So  it  is  with  flotation. 

In  the  laboratory,  it  is  possible  to  use  larger  particles.  The 
following  experiments  were  conducted  in  the  Case  School  of  Applied 
Science  on  material  sized  through  20  and  30-mesh  screens.  The 
phenomena  connected  with  preferential  flotation  furnish  new  evidence 
to  strengthen  the  electrical  theory. 

The  simplest  experiment,  demonstrating  preferential  flotation,  may 
be  performed  as  follows:  Upon  a  4-inch  watch-glass,  place  a  little 
galena,  blende,  and  quartz,  of  20  to  30-mesh  size.  Add  dilute  nitric 
acid  and  place  the  glass  under  a  miscroscope.  The  acid  attacks  the 
galena,  forming  bubbles  of  H2S  gas  that  adhere  to  the  galena.  The 
particles  of  galena  are  electrified  also,  as  can  be  seen  by  the  actions 
of  the  particles.  The  blende  and  quartz  are  not  attacked.  If  the 
ore  had  been  finely  pulverized  and  dilute  nitric  acid  added,  the 
bubbles  of  H2S  would  have  been  sufficient  to  float  the  galena,  leaving 
the  blende  and  quartz  at  the  bottom.  However,  with  fine  particles, 
some  blende  and  quartz  would  have  been  entrapped,  brought  to  the 
surface,  and  held  there  by  surface  tension.  The  bubbles  are  not 
sufficient  to  float  the  coarse  galena,  but  by  a  vanning  motion  of  the 
glass,  the  galena  will  collect,  being  brought  and  held  together  by 
the  H2S  bubbles,  forming  a  mat,  which  is  lighter  than  quartz  or 
blende  and  can,  therefore,  be  panned  off,  leaving  the  blende  and 
quartz.  This  experiment  seems  to  show  that  the  H2S  is  charged 
oppositely  to  the  galena. 

If  more  concentrated  nitric  acid  had  been  added  to  the  ore, 
the  blende  would  have  been  attacked  and  the  process  would  have 
been  reversed,  the  blende  forming  the  mat  while  galena  and  quartz 


THE  ELECTRICAL  THEORY  OF  FLOTATION II  259 

were  left  behind.  If  dilute  sulphuric  acid,  one  part  of  acid  to  four 
of  water,  had  been  used,  then  both  the  blende  and  galena  would 
have  been  attacked  and  if  the  ore  had  been  finely  pulverized,  no 
'preferential'  separation  would  have  resulted,  both  galena  and  blende 
finding  their  way  into  the  float  concentrate.  However,  with  coarse 
material,  the  blende  is  much  more  highly  charged  than  the  galena 
and  if  the  watch-glass  be  tapped  and  the  contents  given  a  vanning 
motion,  the  blende  will  gather  most  of  the  H2S  bubbles  and  finally 
float,  leaving  galena  and  quartz  behind.  This  shows  that  the  elec- 
trification of  minerals  varies  with  different  acids  and  also  with 
different  strengths  of  the  same.  This  action  of  one  mineral,  'robbing7 
the  others  of  their  bubbles,  has  riot  been  utilized  in  practice,  as  yet, 
but  there  is  no  reason  why  'preferential'  separations  could  not  be 
made  on  a  large  scale,  utilizing  this  principle.  Less  air  or  gas 
would  be  necessary  than  in  the  present  type  of  frothing-cells  and  a 
clean  concentrate  would  be  produced  at  once.  A  separation  of 
blende,  galena,  .pyrite,  and  quartz  may  be  made  as  follows : 

Add  dilute  sulphuric  acid  and  pan  off  the  blende ;  then  add  dilute 
nitric  acid  and  pan  off  the  galena;  then  add  concentrated  sulphuric 
or  nitric  acid,  which  attacks  the  pyrite  so  that  it  may  be  panned  off. 

Or  the  separation  may  be  made  with  nitric  acid  alone,  varying 
the  strengths;  with  sulphuric  acid,  by  use  of  the  'robbing'  action 
described  above  or  by  use  of  hydrochloric  and  other  reagents  that 
attack  one  or  another  of  the  minerals  more  strongly  than  the  others. 
If  galena  or  blende  and  magnetite  be  treated  with  dilute  sulphuric 
acid,  the  magnetite  will  not  be  acted  upon  by  the  acid,  but  some  of 
the  H2S  bubbles  generated  by  the  sulphide  will  attach  themselves  to 
the  magnetite,  provided  the  bubble  is  formed  near  the  magnetite. 
This  illustrates  the  fact  that  electrical  conductors  in  a  conducting 
liquid  attract  electrified  bubbles.  A  slight  jar,  however,  will  displace 
these  bubbles;  or  a  piece  of  sulphide  in  close  proximity  will  rob  the 
magnetite  of  the  bubble,  magnetite  being  a  poor  conductor. 

Referring  to  the  article  on  page  668  of  the  Mining  and  Scientific 
Press  of  October  30,  1915,  describing  a  patent  for  preferential 
flotation  of  blende,  galena,  and  pyrite,  the  second  paragraph  reads: 
"The  new  process  consists  of  treating  ores  in  a  medium  (i.  e.  sulphuric 
acid  and  sodium  sulphite)  that  wets  the  zinc  sulphide  and  which  does 
not  wet  the  lead  sulphide  or  pyrite."  This  phenomenon  brings  out 
nicely  the  part  played  in  flotation  by  the  "dielectric  film."  When 
thio-sulphates,  sulphites,  or  bi-sulphites  are  acted  upon  by  sulphuric 
acid,  there  is  more  to  the  phenomenon  than  formation  of  S02  gas. 


260  THE  FLOTATION  PROCESS 

The  following  reactions  take  place  when  blende  and  galena  are  treated 
with  sulphuric  acid  and  sodium  sulphide: 

ZnS  +  PbS  +  2H2S04  =  ZnS04  +  PbS04  +  2H2S 

*Na2S03  +  H2S04  =  Na2S04  +  H20  +  S02 

f2H2S  +  S02  =  2H20  +  3S 

This  sulphur  thus  formed  is  in  a  very  fine  state  and  acts  as  a 
dielectric  film  about  the  galena,  for  which  it  has  a  great  attraction. 
Therefore,  no  frothing  agent  is  needed  in  this  case,  as  the  dielectric 
film  about  the  bubbles  is  formed  by  the  sulphur  similarly  to  the 
films  of  oil  formed  in  the  ordinary  flotation  processes.  In  the  last 
paragraph  of  the  above-mentioned  article  on  'Preferential  Flotation,' 
the  statement  is  made  that  "the  procuring  of  the  effect  aimed  at,  is 
dependent  upon  the  presence  of  a  frothing  agent,  only  when  a 
Deducing  gas  is  introduced  into  the  medium.  It  is  not  dependent 
on  the  presence  of  a  frothing  agent  in  the  flotation  medium,  when 
a  reducing  gas  is  generated  in  the  flotation  medium  by  a  reaction  of 
a  substance  introduced  into  it."  In  other  words,  if  sulphur  or  any 
other,  'dielectric'  is  liberated  in  a  very  fine  state,  by  a  "reaction  of 
a  substance  introduced,"  no  frothing  agent  need  be  used. 

This  action  may  be  nicely  illustrated  by  taking  20  to  30-mesh 
galena  and  blende  and  treating  them  with  dilute  nitric  acid  on  a 
watch-glass  and  observing  the  result  under  a  microscope.  The  galena 
will  gather  all  the  H2S  bubbles,  when  vanned.  Now  if  the  sulphuric 
acid  is  added  and  the  watch-glass  be  tapped  and  the  particles  moved 
over  one  another,  the  H2S  bubbles  on  the  galena  will  be  robbed  by 
the  blende.  Sulphur  may  be  seen  surrounding  the  bubbles,  the 
reaction  being  as  follows: 

ZnS  +  PbS  +  2H2S04  =  ZnS04  +  PbS04  +  2H,S 

(1)  H2S  +  H2S04  =  S02  +  2H20  +  S 

(2)  2H2S  +  S02  =  2H20  +  3S 

In  (1),  the  sulphur  is  formed  from  the  decomposition  of  H2S ; 
and  would  be  charged  oppositely  to  the  sulphur  formed  by  the 
decomposition  of  S02  gas.  In  (2),  we  have  both  negatively  and 
positively  charged  sulphur  particles. 

The  larger  bubbles,  with  sulphur  particles  adhering  to  them,  may 
burst  on  reaching  the  surface  and  their  film  of  sulphur  will  spread 


Newth's  'Inorganic  Chemistry,'  p.  417. 
p.  436. 


THE  ELECTRICAL  THEORY  OF  FLOTATION II  261 

over  the  water.  If  particles  of  mineral  had  been  attracted  to  the 
bubble,  then  these  particles  would  have  remained  attached  to  the 
sulphur  film,  even  after  disruption  of  the  bubble,  showing  the  electri- 
fication of  the  dielectric  film.  The  same  phenomenon  occurs  when 
the  film  is  a  liquid  dielectric,  like  oil. 

The  laboratory  tests  with  chemical  reagents  generating  H2S  gas 
give  the  opposite  results  from  the  regular  air-bubble  flotation.  The 
ordinary  flotation  method  in  practice  is  to  add  a  little  acid  and 
frothing  agent  to  the  pulp.  The  sulphides  are  positively  charged  by 
friction,  while  the  frothing  agent  and  air  are  charged  negatively. 
The  oil  surrounds  the  sulphides,  but  the  film  is  so  thin  that  the 
negatively-charged  bubble  is  attracted  by  the  positively-charged 
sulphide.  If  the  film  of  oil  is  too  thick,  the  attraction  between  the 
sulphide  and  bubble  is  too  feeble,  and  flotation  fails. 

In  the  laboratory,  H2S  is  charged  positively,  but  the  sulphides 
are  charged  negatively  by  chemical  action.  So  the  bubble  attaches 
itself  to  the  electrified  sulphide. 

In  preferential  flotation  of  galena  and  blende,  in  practice,  the 
ore  is  treated  with  H2S04  and  Na2S03.  Sulphur  is  liberated  and 
the  galena  is  coated  with  the  particles  of  sulphur  positively-charged, 
while  the  negatively-charged  sulphur  coats  the  gas  bubbles.  The 
negatively-charged  air  bubbles  of  the  flotation  machine  attach  them- 
selves to  the  positively-charged  sulphur  coating  the  galena  and  repel 
the  negatively-charged  blende. 

In  the  laboratory  experiments,  the  H2S  bubbles  are  charged 
positively  and  are  attracted  to  the  negatively-charged  blende  and 
repelled  by  the  positively-charged  sulphur  on  the  galena.  In  this 
case,  the  blende  is  floated.  When  H2S  is  blown  into  the  pulp  in 
practice,  no  sulphur  is  formed — the  H2S04  solution  being  too  weak 
for  this  reaction.  Therefore,  to  make  a  persistent  froth,  a  frothing 
agent  must  be  added  to  the  pulp. 

In  conclusion,  it  may  be  well  to  call  attention  to  the  fact  that 
for  laboratory  experiments  in  preferential  flotation,  any  one  of  the 
sulphides  may  be  separated  from  the  other  sulphides,  (a)  by  the  use 
of  some  reagent  that  attacks  this  particular  sulphide  and  not  the 
others,  (Z>)  by  the  use  of  a  reagent  that  attacks  one  sulphide  more 
vigorously  than  the  others;  in  this  case,  the  vanning  motion  allows 
the  sulphide  more  highly  charged  to  gather  up  the  bubbles  from  the 
sulphides  less  highly  charged,  and  if  sufficient  buKbles  are  collected, 
the  mass  of  bubbles  and  sulphide  will  float.  If  not  sufficiently  buoyed, 
the  mass  remains  submerged,  but  it  is  lighter  than  the  other  sulphides 


262  THE  FLOTATION  PROCESS 

or  gangue  minerals  and  can  be  panned  off  or  separated  by  hydraulic 
classification. 

The  second  point  of  interest  is  the  formation  of  a  frothing  agent, 
within  the  pulp,  when  reactions  take  place  that  liberate  dielectric 
substances  in  a  very  fine  state,  electrically  charged. 

The  third  .point  is  that  laboratory  experiments  may  not  work 
out  in  practice,  due  to  failure  to  understand  the  nature  of  the 
electrical  charges  of  the  bubbles,  dielectrics,  and  particles  of  ore.  A 
little  stronger  reagent  or  a  different  way  of  frictionally  electrifying 
the  bubbles  and  pulp,  or  too  thick  a  film  of  dielectric  or  frothing 
agent  causes  the  attraction  to  cease  or  change.  It  is  no  wonder  that 
great  difficulty  has  been  experienced  in  the  practical  application 
of  flotation  to  ores,  when  such  delicate  electric  forces  have  to  be 
considered. 


EFFECTS  OF  SOLUBLE  COMPONENTS  OF  ORE  ON  FLOTATION     263 

EFFECTS  OF  SOLUBLE  COMPONENTS  OF  ORE  ON 

FLOTATION 

By  AN  OCCASIONAL  CORRESPONDENT 
(From  the  Mining  and  Scientific  Press  of  December  18,  1915) 

In  concentration  by  flotation,  the  soluble  components  of  an  ore 
may  play  an  important  role.  Occasionally  ores  that  are  shown  by 
preliminary  test  to  be  unsuitable  for  flotation  may  be  treated  by  the 
process  after  the  soluble  ingredients  have  been  removed  by  decan- 
tation.  On  the  other  hand,  excellent  results  may  be  obtained  on 
certain  ores  by  flotation  in  fresh  water ;  but  when  the  water  is  fouled 
by  successive  contact  with  fresh  lots  of  ore  (as  is  often  the  case 
in  mill-practice)  the  results  may  be  far  from  satisfactory. 

This  article  deals  with  a  determination  of  the  fouling  agents 
in  a  certain  ore,  and  outlines  methods  for  overcoming  such  fouling 
efforts.  Since  all  tests  were  made  on  ore  from  a  single  mine,  the 
results  cannot  be  regarded  as  generally  applicable;  however,  it  is 
hoped  that  the  experience  recorded  here  may  be  of  some  interest 
to  others  studying  similar  problems  in  flotation. 

The  tests  were  made  on  a  silicified-rhyolite  ore  assaying  silver 
37  oz.,  gold  0.15  oz.,  lead  1%,  copper  0.25%,  and  zinc  1.5%.  The 
principal  minerals  were  argentiferous  sphalerite,  argentiferous  galena, 
and  stromeyerite.  The  value  lay  almost  entirely  in  silver.  For  this 
reason,  only  silver  assays  are  here  recorded.  Sufficient  analyses 
were  made  to  indicate  that  the  concentration  of  zinc,  lead,  and 
copper  roughly  paralleled  that  of  silver. 

Preparatory  to  making  the  tests,  a  large  general  sample  of  ore 
was  ground  to  pass  a  200-mesh  screen,  and  thoroughly  mixed.  In 
each  test,  a  200-gram  portion  of  the  general  sample  was  emulsified 
with  one  litre  of  water  and  0.05%  of  crude  pine-oil.  The  mixture 
was  then  treated  for  a  half -hour  in  an  experimental  flotation  machine, 
consisting  of  an  agitation-chamber  connected  in  such  a  manner  with 
a  concentrate-separation  chamber,  as  to  permit  of  repeated  treatment 
of  the  tailing.  Results  in  a  flotation  plant  treating  this  ore  roughly 
checked  the  work  in  the  experimental  machine. 

Preliminary  tests  showed  that  when  the  ore  was  treated  by 
flotation  in  fresh  water,  the  tailing  assayed  13  oz.  silver  and  the 
concentrate  assayed  440  oz.  per  ton.  When  the  water  used  in  the 
first  test  was  removed  by  filtration  and  re-used  on  a  second  test, 
the  tailing  assayed  18  oz.,  and  the  concentrate  240  oz.  When  the 


264  THE  FLOTATION  PROCESS 

same  water  was  re-used  a  third  time  on  a  fresh  sample  of  ore,  the 
tailing  assayed  27  oz. ;  the  concentrate,  190  oz.  Evidently  some 
extremely  deleterious  substances  had  been  dissolved  from  the  ore. 
An  analysis  was  made  of  the  water  filtered  from  the  third  test,  with 
the  following  results: 

Iron  (ferric)   . Tr. 

Iron  (ferrous)  -      0.002% 

Aluminum    Tr. 

Calcium    Nil 

Magnesium  oxide 0.012% 

Sulphur  0.020% 

Manganese    0.001% 

Potassium  and  sodium 0.010% 

Copper Tr. 

Most  of  the  soluble  minerals  were  present  as  sulphates. 

The  next  step  was  to  determine  the  effect,  on  flotation,  of  the 
various  sulphates. 

Sodium  and  potassium  sulphates,  when  added  to  fresh  tests  in 
the  proportion  indicated  in  the  analysis,  yielded  a  13  oz.  tailing  and 
a  650  oz.  concentrate ;  thus  producing  a  marked  increase  in  the  grade 
of  concentrate  without  detrimental  effect  on  the  tailing.  ! 

Manganese,  magnesium,  and  ferric  sulphates  produced  no  effect 
when  added  in  the  proportions  indicated;  in  larger  amounts,  mag- 
nesium sulphate  was  harmful  and  ferric  sulphate  beneficial. 

Ferrous  sulphate  proved  extremely  injurious  to  flotation.  When 
present  as  above  recorded,  a  20  oz.  tailing  and  a  240  oz.  concentrate 
were  produced.  When  a  small  amount  of  copper  sulphate  was 
added  to  the  same  quantity  of  ferrous  sulphate,  the  tailing  assayed 
25  oz.,  and  the  concentrate  200  oz.  Evidently  ferrous  and  copper 
sulphates  were  the  principal  fouling  agents  in  the  original  tests. 

It  was  necessary  to  devise  means  for  correcting  the  effects  of  these 
sulphates. 

First :  sufficient  sulphuric  acid  and  hydrogen  peroxide  were  added 
to  a  charge  containing  ferrous  sulphate^to  convert  the  ferrous  sulphate 
to  the  ferric  state.  The  tailing  from  this  charge  assayed  11  oz.,  and 
the  concentrate  800  oz.  With  the  same  amount  of  acid,  but  using 
no  peroxide,  the  tailing  assayed  14  oz.,  and  the  concentrate  780  oz. 
Evidently  the  acid  increased  the  grade  of  concentrate  and  also 
decreased  the  injurious  effects  of  the  ferrous  sulphate  upon  extraction. 

Second :  efforts  were  made  to  precipitate  the  ferrous  and  copper 
sulphate.  A  test,  containing  these  sulphates  in  the  proportions 
indicated  in  the  analysis,  was  rendered  slightly  alkaline  by  the 


EFFECTS  OF  SOLUBLE  COMPONENTS  OF  ORE  ON  FLOTATION     265 

addition  of  lime  hydrate.  The  tailing  assayed  12  oz.,  and  the 
concentrate  450  oz.  When  sodium  hydrate  was  used  in  place  of 
lime,  the  tailing  assayed  8  oz.,  and  the  concentrate  600  oz.  With 
the  iron  precipitated  by  sodium  carbonate,  the  tailing  assayed  6  oz., 
and  the  concentrate  800  oz.  With  a  combination  of  lime  hydrate 
and  sodium  carbonate,  the  concentrate  assayed  800  oz.,  and  the  tailing 
3  oz.  Evidently  the  use  of  hydrates  and  carbonates  produces  much 
better  results  than  can  be  secured  by  acid.  The  cost  of  sodium 
hydrate  and  sodium  carbonate,  and  the  injurious  effects  of  the  latter 
upon  settling  and  filtration,  restricts  the  use  of  these  chemicals. 
Lime  hydrate,  on  the  other  hand,  presents  a  cheap  and  efficient 
means  for  preventing  the  accumulation  of  ferrous  sulphate  in  mill- 
solutions.  The  calcium  sulphate  resulting  from  the  reaction  is 
somewhat  detrimental  to  flotation;  a  saturated  solution  yielding  a 
16  oz.  tailing  and  a  450  oz.  concentrate.  In  ordinary  practice  the 
solution  would  be  far  from  saturated,  and  the  results  much  more 
satisfactory. 

The  lime-hydrate  method  has  been  successfully  used  on  this  ore 
in  continuous  mill-tests.  During  flotation  the  alkalinity  was  main- 
tained as  nearly  as  possible  at  0.02  Ib.  lime-oxide  per  ton  of  water. 
After  flotation,  half  the  circuit-water  was  wasted,  the  remaining 
half  being  supplemented  by  fresh  water,  at  the  head  of  the 
mill;  lime  sulphate  thus  being  prevented  from  accumulating  in  the 
solution.  For  a  month  during  which  the  process  was  used,  the 
concentrate  from  the  flotation  plant  averaged  600  oz.,  and  the  tailing 
6  oz.  This  compares  favorably  with  a  20-oz.  tailing  from  gravity 
concentration  and  a  12-oz.  tailing  from  flotation  in  an  acid  solution. 
Aside  from  effecting  better  concentration,  the  lime  method  is  cheaper 
than  the  acid  process  and  is  not  injurious  to  subsequent  cyanidation. 

When  lime  is  used  in  flotation,  extreme  care  must  be  exercised 
in  maintaining  the  proper  alkalinity.  The  table  submitted  herewith 
shows  that  the  best  results,  both  as  regards  extraction  and  grade 
of  concentrate,  are  secured  when  the  alkalinity  during  flotation  is 
extremely  low  (between  0.01  and  0.02  Ib.  CaO  per  ton  of  solution). 
Experiments  indicate  that  alkalinity  is  beneficial  to  flotation  but 
that  the  coagulating  effect  of  high  lime  upon  slime  increases  the 
affinity  of  the  slime  for  the  froth,  lowering  the  grade  of  concen- 
trate. When  the  coagulating  effect  is  counteracted  by  the  addition 
of  sodium  carbonate,  or  when  sodium  hydrate  is  used  in  place  of 
lime,  an  alkalinity  equivalent  to  a  half-pound  of  CaO  per  ton  of 
solution  may  be  maintained  without  harmful  effects  on  flotation. 


266  THE  FLOTATION  PROCESS 

Usually  a  bare  alkalinity  maintained  with  quicklime  produces  equally 
good  results. 

In  order  further  to  study  the  effects  of  copper  sulphate  on  flotation, 
a  solution  containing  0.01%  CuS04  was  employed  in  another  series 
of  tests.  When  this  solution  was  used  alone  the  separation  was 
extremely  poor,  the  tailing  assaying  32  oz.  and  the  concentrate 
100  oz.  When  sufficient  quicklime  was  added  to  produce  a  slight 
alkalinity,  the  tailing  was  reduced  to  24  oz.,  while  the  concentrate 
increased  to  180  oz.  per  ton.  A  further  improvement  was  effected 
by  the  use  of  sodium  hydrate,  a  340  oz.  concentrate  and  an  11  oz. 
tailing  being  secured.  This  was  still  far  from  satisfactory. 

An  attempt  was  made  next  to  precipitate  the  copper  as  sulphide. 
By  employing  hydrogen  sulphide  in  a  solution  rendered  alkaline 
by  lime  hydrate,  a  6  oz.  tailing  and  a  450  oz.  concentrate  were 
obtained.  When  sodium  sulphide  and  sodium  hydrate  were  used, 
the  tailing-assay  was  reduced  to  3  oz.,  and  the  concentrate  increased 
to  700  oz.  These  results  show  that  the  injurious  effect  of  soluble 
copper  may  be  overcome  by  the  use  of  hydrogen  or  sodium  sulphide 
in  conjunction  with  lime  or  sodium  hydrate. 

The  following  conclusions  were  established  for  the  ore  tested: 

1.  Sodium,  potassium,  and  ferric  sulphates  are  rather  beneficial 
to  flotation  than  otherwise. 

2.  Manganese  sulphate  has  practically  no  effect  on  flotation. 

3.  Magnesium  and  calcium  sulphates  are  slightly  harmful,  while 
ferrous  and  copper  sulphate  are  extremely  harmful. 

4.  The  effect  of  magnesium  and  calcium  sulphates  may  be  over- 
come by  the  use  of  sodium  carbonate  in  an  alkaline  solution. 

5.  The  effect  of  ferrous  sulphate  can  be  overcome  by  the  use  of 
sulphuric  acid  or,  better  still,  by  employing  quicklime,  caustic  soda, 
or  sodium  carbonate. 

6.  The  effect  of  copper  sulphate  may  be  overcome  by  the  use 
of  hydrogen  sulphide  or  sodium  sulphide  in  an  alkaline  solution. 

7.  The  use  of  sodium  carbonate,  though   aiding  materially  in 
flotation,  is  of  doubtful  utility  in  plants  where  the  pulp  must  be 
dewatered. 

8.  Lime  hydrate  is  slightly  less  satisfactory  metallurgically  than 
sodium  hydrate  or  sodium  carbonate,  but  the  use  of  it  is  inexpensive 
and  aids  materially  in  settling  and  filtering. 


FLOTATION A  PARADOX  267 

FLOTATION— A  PARADOX 

By  DUDLEY  H.  NORRIS 
(From  the  Mining  and  Scientific  Press  of  December  25,  1915) 

Flotation  is  a  paradox.  In  a  flowing  mixture  of  finely  pulverized 
ore  and  water  it  causes  the  heavy  metallic  sulphides  to  float  to  the 
surface,  where  they  are  collected  for  further  metallurgical  treatment, 
while  the  light  barren  gangue  sinks  to  the  bottom  and  is  run  into 
the  tailing-pond. 

This  apparent  reversal  of  the  attraction  of  gravitation  is  due 
to  the  introduction  into  the  flowing  mixture  of  a  small  quantity 
of  oil  or  other  emollient  in  such  a  manner  that  every  particle  of 
the  ore,  whether  metallic,  or  gangue,  is  brought  into  contact 
with  the  oil,  whereupon  there  is  what  seems  a  selective  action  between 
the  oil  and  the  metallic  particles  such  that  these  become  coated 
with  the  oil,  whereas  there  is  no  such  action  of  the  oil  upon  the 
gangue.  Under  proper  conditions,  at  or  about  the  same  time  that 
this  oil  coating  of  the  metallic  particles  takes  place,  there  may  be 
caused  to  appear  in  the  flowing  mixture  bubbles  of  air.  These  attach 
themselves  to  the  oil-coated  metallic  particles  and  stick  to  them  with 
more  or  less  tenacity,  making  a  new  entity  consisting  of  metallic 
particle,  oil-coating,  and  air-bubble.  The  specific  gravity  of  this  entity 
is  less  than  that  of  the  water  of  the  flowing  mixture;  thereupon, 
because  of  the  attraction  of  gravitation,  and  not  in  spite  of  it,  the 
heavy  metallic  sulphides  float  to  the  surface  and  the  comparatively 
light  gangue  sinks  to  the  bottom,  neither  oil  nor  bubbles  having  any 
tendency  to  attach  themselves  to  the  barren  gangue. 

My  interest  in  flotation  arose  from  the  accumulation  at  my  mine, 
the  Magistral,  at  Zacatecas,  Mexico,  of  a  couple  of  hundred  thousand 
tons  of  chalcopyrite  ore  of  low  grade  which  I  had  tried  unsuccessfully 
to  treat  by  water  concentration.  I  came  to  San  Francisco  in  February 
1905  and  went  to  London  in  June  1906,  to  investigate  the  two 
Elmore  processes.  I  sent  some  of  my  ore  to  London  and  the  tests 
showed  a  saving  of  90%  or  more  by  the  vacuum  process.  I  set  up 
an  Elmore  laboratory  plant  at  the  Magistral  mine,  9000  ft.  above 
sea-level,  but  got  no  satisfactory  results — I  judged  that  the  altitude 
acted  as  a  partial  vacuum  and  that  there  was  no  air  left  in  solution 
in  the  water.  I  then  led  a  small  pipe  from  the  air-compressor  and, 
tying  a  folded  pocket-handkerchief  over  the  end  of  the  pipe,  fed 
compressed  air  into  the  flowing  mixture  through  16  thicknesses  of 


268  THE  FLOTATION  PROCESS 

fine  linen,  150  threads  to  the  inch.  I  found  that  with  a  light 
pressure  of  air  the  bubbles  coalesced  on  coming  through  the  fabric 
and  when  released  and  started  on  their  upward  journey  were  of  a 
uniform  size,  about  that  of  a  marrow-fat  pea.  With  greater  pressure 
the  size  of  the  bubbles  was  reduced,  but  the  action  of  the  air  was 
so  violent  that  the  mixture  was  like  a  boiling  geyser  and  everything, 
ore  and  gangue  alike,  was  brought  to  the  surface.  Thereafter  my 
flotation  experiments  were  suspended  until  one  day  in  a  Pullman  car 
on  the  Mexican  Central  railroad  I  drew  some  water  into  the  hand 
wash-basin  and  I  noticed  that  it  was  as  white  as  milk,  but  presently 
became  just  ordinary  transparent  water.  I  saw  at  one  that  this  was 
due  to  an  artificial  aeration  of  the  water  in  the  tank  under  the  car, 
and  when  the  train  stopped,  I  read  from  the  gauge  that  the  pressure 
in  the  tank  was  11  atmospheres.  That  seemed  to  be  a  solution  of 
the  problem  of  the  lack  of  air  in  the. water  of  the  Elmore  process; 
so  I  patented  the  method,  together  with  the  apparatus  for  utilizing 
the  same. 

It  is  not  proposed  here  to  discuss  any  theories  of  flotation,  surface 
tension,  ions  or  static  or  electric  conditions  or  to  explain  phenomena, 
of  which  we  at  least  know  a  little,  in  terms  of  something  of  which 
we  know  less.  Instead  of  that,  a  classification  is  suggested,  homely 
and  commonplace  in  its  terms,  but  which  will  impress  upon  anyone 
the  exact  limitations  of  each  kind  of  flotation. 

The  oldest  flotation  is  that  including  Everson,  Froment,  and 
others,  and  the  Minerals  Separation.  It  produces  an  ''agitation  to 
form  a  froth"  and  is  exactly  duplicated  by  the  activity  of  the  cook 
with  a  Dover  egg-beater  stirring  what  she  is  apt  to  call  an  "egg- 
omelette." 

Then  there  are  the  Australian  processes  known  as  the  De  Bavay 
and  the  Delprat,  where  an  acid  acts  upon  an  alkaline  carbonate  and 
releases  the  carbonic  acid  gas,  which  action  is  duplicated  in  common 
life  by  the  efficient  Seidlitz  powder. 

Then  there  is  the  Elmore,  which  gets  from  ordinary  water  the 
air  that  the  goldfish  in  the  aquarium  gets,  and  no  more. 

Then  there  are  the  Callow  and  the  Towne  processes,  where  air 
is  forced  through  a  porous  medium,  as  above  described ;  and,  finally, 
the  Norris  process,  which  utilizes  the  air  dissolved  in  water  under 
pressure,  as  seen  in  the  Pullman  car  or  in  the  water-service  at  many 
places  on  the  eastern  shore  of  San  Francisco  Bay. 

I  believed  that  I  had  discovered  a  basic  principle  in  flotation, 
and  in  September  1906  I  applied  for  U.  S.  patents  on  the  method 


FLOTATION A  PARADOX  269 

and  on  the  apparatus  for  using  the  Pullman  bubbles  in  notation; 
later  I  took  out  patents  in  ten  foreign  countries  on  the  same  basis. 
Continuing  my  metallurgical  investigation  in  the  summer  of  1907, 
I  went  to  nearly  all  the  principal  copper-concentrating  mills  in 
Colorado,  Utah,  and  Arizona,  and  to  Cananea.  I  saw  all  the  stars 
of  the  first  magnitude  in  the  copper  metallurgical  firmament,  but 
they  shed  no  light  on  flotation.  In  fact,  I  was  asked  how  the  word 
was  spelled.  The  net  result  was  that  I  went  back  to  Zacatecas  and 
later  built  the  Magistral  smelter.* 

About  this  time  I  received  word  from  my  patent  attorneys  that  I 
was  opposed  in  the  London  patent-office  by  the  Minerals  Separation ; 
but  I  instructed  them  not  to  appear  and  the  case  went  on  without 
me,  as  will  be  seen  by  the  decision  in  the  case  where  it  is  cited  that 
"At  the  hearing  Mr.  Ballantyne  appeared  for  the  opponents;  the 
applicant  was  not  represented."  Notwithstanding  the  fact  that  the 
opposition  had  things  all  their  own  way,  the  London  patent-office 
over-ruled  the  opposition  and  decided  in  favor  of  issuing  my  patent, 
and  when  the  Minerals  Separation  appealed  to  the  law-officer  the 
decision  was  affirmed,  on  February  24,  1910,  and  the  British  patent 
duly  issued  to  me. 

In  the  recent  case  of  Minerals  Separation  against  Miami,  counsel 
for  plaintiff  said  that  the  defendant  interpreted  the  older  patents, 
not  in  the  light  of  the  state  of  the  art  at  the  time  the  respective 
patent  was  applied  for,  but  in  the  light  of  later  developments.  It 
so  happens  that  a  reference  to  the  decision  in  Minerals  Separation 
v.  Norris  before  the  British  patent  authorities,  shows  that  the 
Minerals  Separation  is  now  doing  that  very  thing. 

My  British  application  was  dated  June  27,  1907,  and  was  opposed 
by  the  Minerals  Separation  on  the  grounds  of  prior  British  patents, 
as  follows: 

No.  12;776  A.D.  1905— Froment 
No.  29,283  1904— Elmore 

No.     7,803  1905— Sulman 

No.  26,712  1905— Sulman 

No.  13,268  1907— Hoover 

These  include  the  British  patents  corresponding  to  some  of  the 
American  patents  on  the  basis  of  which  the  Minerals  Separation 
sued  Hyde  and  Miami  in  the  United  States  courts,  and  the  suits  are 
now  pending.  The  case  in  the  British  patent-office  was  decided,  and 


*See  'The  Copper  Handbook,'  1912,  page  545. 


270  THE  FLOTATION  PROCESS 

% 

the  decision  bears  date,  March  15,  1909.  Consequently  the  position 
of  the  Minerals  Separation  as  to  the  basis  of  their  patent  rights  as 
stated  in  the  case  against  me,  between  June  27,  1907,  and  March  15, 
1909,  is  the  true  statement  of  their  own  idea  of  their  rights  and 
position  and  not  that  set  up  in  the  later  cases  some  years  after, 
and  in  the  light  of  the  more  mature  experience  which  is  protested 
by  Minerals  Separation  itself  when  used  by  the  Miami  company. 

Here  is  the  Minerals  Separation  position  in  the  case  against  Norris, 
as  appears  in  the  decision,  which  says  that  Mr.  Ballantyne  relied 
mainly  on  the  Sulman  and  Hoover  patents.  He  contended  that  the 
underlying  idea  of  the  various  processes  is  asserted  in  Claim  No.  1 
of  the  Sulman  patent,  that  is,  introducing  by  some  means  or  other 
air  under  pressure  into  pulp  containing  oil  and  water  and  then 
allowing  the  pulp  to  come  into  a  vessel  which  is  open  at  the  top  to  the 
atmosphere. 

Claim  No.  1  of  the  American  Sulman  patent  "  consists  in  mixing 
the  powdered  ore  with  water,  adding  a  small  proportion  of  an  oily 
liquid  having  a  preferential  affinity  for  metalliferous  matter 
(amounting  to  a  fraction  of  \%  on  the  ore)  agitating  the  mixture 
until  the  oil-coated  mineral  matter  forms  into  a  froth  and  separating 
the  froth  from  the  remainder  by  flotation."  There  is  no  hint  in 
Mr.  Ballantyne 's  presentation  of  his  case  before  the  London  patent- 
office  that  he  or  his  client,  the  Minerals  Separation,  placed  any 
importance  upon  the  little  phrase  in  parenthesis  (amounting  to  a 
fraction  of  1%  on  the  ore)  and  it  can  hardly  be  imagined  that  any 
court  would  permit,  at  this  late  day,  a  substitution  of  another  idea 
for  what  Mr.  Ballantyne  claimed,  in  the  case  against  Norris,  to  be 
the  underlying  idea  of  the  various  processes. 

The  decision,  in  my  favor,  contained  these  words:  "It  appears 
to  me  therefore,  that  the  applicant  is  entitled  to  a  patent  for  his 
invention****!  decide  therefore  to  seal  a  patent  on  the  applica- 
tion***/' The  Minerals  Separation  appealed,  but  the  decision  was 
affirmed  and  the  patent  issued  February  24,  1910.  The  Federal 
Circuit  Court  of  Appeals,  on  appeal,  decided  the  Hyde  case  against 
the  Minerals  Separation,  in  these  words: 

"We  hold  that  to  sustain  the  appellee's  patent  would  be  to 
give  to  the  owners  thereof  a  monopoly  of  that  which  others  had 
discovered.  "What  they  claim  to  be  the  new  and  useful  feature  of 
their  invention,  as  stated  by  their  counsel,  is  agitating  the  mixture 
to  cause  the  oily-coated  mineral  to  form  a  froth.  As  we  have  seen, 
that  feature  was  clearly  anticipated  by  the  prior  art,  and  when  the 


FLOTATION A  PARADOX  271 

elements  of  the  appellee's  claims  are  read  one  by  one,  it  will  be 
found  that  each  step  in  their  process  is  fully  described  in  more  than 
one  of  the  patents  of  the  prior  art,  with  the  single  exception  of  the 
reduced  quantity  of  oil  which  they  use." 

The  judgment  of  the  court  below  was  reversed  by  the  Circuit 
Court  of  Appeals  and  a  motion  for  a  re-hearing  was  denied.  Then 
the  Minerals  Separation  applied  to  the  U.  S.  Supreme  Court  for  a 
writ  of  certiorari,  which  was  granted,  and  the  case  is  now  before 
that  court.  The  Minerals  Separation  advertised  that  the  Supreme 
Court  had  granted  their  petition,  without  going  into  details  as  to 
just  what  the  petition  was.  As  a  matter  of  fact,  the  granting  of  a 
writ  of  certiorari  by  the  Supreme  Court  is  in  no  sense  a  decision 
on  the  merits  of  the  case. 

Prior  to  1891  an  appeal  to  the  Supreme  Court  from  a  Circuit 
Court  was  a  matter  of  course,  if  the  sum  involved  reached  $1000, 
the  result  being  a  crowded  calendar,  years  behind.  In  1891  the 
Judiciary  Act  abolished  the  Circuit  Courts,  merging  their  functions 
in  the  District  Courts,  and  creating  the  Circuit  Courts  of  Appeals 
with  final  jurisdiction  in  many  classes  of  cases,  including  patents. 
The  Act  provided  for  a  writ  of  certiorari  in  cases  where  the  judg- 
ment of  the  Circuit  Court  of  Appeals  is  final  and  the  rules  of  the 
Supreme  Court  say  that  the  writ  will  issue  where  cases  of  great 
gravity  or  importance  are  involved. or  where  two  different  Circuit 
Courts  of  Appeals  have  rendered  conflicting  decisions. 

The  proceedings  on  the  application  are  very  technical.  A  petition 
must  be  presented  setting  forth  the  facts  of  the  case  together  with 
the  reasons  for  the  writ.  Two  weeks  notice,  or  west  of  the  Rocky 
Mountains,  three  weeks,  to  the  adversary;  and  no  petition  will  be 
granted  within  a  fixed  time  before  the  end  of  the  term.  With  the 
petition  must  be  filed  a  certified  copy  of  the  papers  on  which  the 
court  below  acted  and  30  copies  uncertified.  No  oral  argument  is 
allowed.  As  Chief  Justice  Fuller  expressed  it:  "The  inquiry  upon 
the  application  is  whether  the  matter  is  of  sufficient  importance  in 
itself  and  sufficiently  open  to  controversy  to  justify  the  writ." 

At  the  October  term  of  1914,  at  which  the  petition  for  the 
Minerals  Separation  writ  was  granted,  there  were  45  applications 
for  writs  of  certiorari,  of  which  11  were  granted  and  34  denied. 
In  the  reports  no  reason  is  given  for  the  Court's  action  in  deciding 
petition  for  certiorari;  but  it  is  extremely  probable  that  a  certain 
number  of  the  applications  were  denied  because  the  technical  require- 
ments of  the  rules  were  not  observed.  That  is  about  the  gist  of 


272  THE  FLOTATION  PROCESS 

the  present  state  of  the  Hyde  case.  There  has  been  no  pardon  nor 
commutation  nor  reversal,  but  merely  a  stay  of  execution. 

The  Minerals  Separation  also  advertised  that  they  had  36  patents 
on  flotation,  suggesting  that  their  collection  includes  about  all  the 
flotation  patents  that  have  any  real  value.  Unfortunately  for  this 
view,  there  is  a  letter  in  existence  written  by  the  Minerals 
Separation  which  says:  "It  is  our  custom  to  add  flotation  patents 
to  our  collection  if  they  can  be  obtained  reasonably  whether  they 
are  of  any  immediate  importance  to  us  or  not."  That  being  their 
custom  and  the  decision  of  the  Circuit  Court  of  Appeals  being  so 
strongly  against  them,  the  inference  is  irresistible  that  however  little 
these  waifs  and  strays  of  patents  were  bought  for,  they  were  not 
worth  it. 

One  can  understand  the  keen  regret  on  the  part  of  the  Minerals 
Separation  that  their  Froment  process  had  not  been  patented  in 
this  country,  but  only  in  Italy  and  England.  They  started  with 
the  Cattermole  process,  which  was  not  a  success,  and  acquired  the 
Froment  afterward.  The  Cattermole,  using  4  to  6%  of  oil,  was 
an  improvement  on  the  Elmore,  which  used  more.  They  acquired 
the  Froment,  which  was  a  bubble  process  as  against  the  processes 
using  only  oil,  and  then  began  a  new  series  of  American  applications 
for  patents.  The  attempts  of  the  Minerals  Separation  to  get  a 
foothold  in  this  country  for  their  process  of  flotation  by  "agitation 
to  form  a  froth"  begin  with  835,120  Sulman  et  al.,  dated  November  6, 
1906.  This  contained  the  agitation-to-form-a-froth  idea  but  it  is 
crudely  worked  out.  Next  came : 

953,746.  Hoover,  April  5, 1910,  with  three  beaters  in  an  agitation- 
vessel  ;  but  this  claims  only  one  in  patent  for  apparatus.  Next  came 

955,012.  Sulman,  April  12,  1910,  for  process  corresponding  to 
Hoover's  apparatus.  Then 

955,857.  Hoover,  December  27,  1910,  claims  mixing-vessel,  an 
agitator  therein,  spitzkasten;  also,  a  secondary  mixing- vessel.  Then 

1,064.209.  Hebbard,  June  10,  1913.  Claim  1.  Apparatus  for 
ore  concentration  by  gas  flotation,  consisting  of  two  adjacent  mixing- 
vessels  each  containing  a  rotating  agitator  and  a  spitzkasten  con- 
tiguous. Claims  3,  4,  and  5  cover  a  number  of  these  elements. 

1,067,485.  Nutter  et  al.,  July  15,  1913.  Process  for  concentrating 
ores  consisting  of  agitating  water  containing  mineral-frothing  agent, 
removing  the  froth,  agitating  pulp  again  with  addition  of  another 
agent,  producing  another  froth,  "and  so  on." 

1,084,196.    Broadbridge  et  al,  January  13,  1914.    Apparatus  for 


FLOTATION A  PARADOX  273 

agitation-frothing  process  comprising  a  series  of  agitating  and  aerating 
vessels  and  a  series  of  spitzkastens. 

1,101,506.  Bradford,  June  23,  1914.  Introduces  flowing  mixture 
from  mixer  into  a  centrifugal  pump,  adding  sulphuric  acid  and  air 
and  steam.  Agitates  to  form  a  froth. 

In  all  these  patents  the  Minerals  Separation  is  the  assignee  and 
the  gradual  advance  is  noticeable  from  the  first  claim  of  one  vessel 
to  the  next  claim  for  two  mixing-vessels,  then  one  agitation  and 
another,  "and  so  on."  How  far  on  is  "so  on"?  Do  they  claim  to 
use  a  third  and  a  fourth  vessel,  and  if  so,  must  they  use  a  different 
"mineral  frothing  agent"  every  time,  or  can  they  repeat  with  the 
same  one?  By  the  way,  just  what,  in  a  strictly  legal  sense,  is  a 
"mineral  frothing  agent"?  Does  this  cover  any  further  discovery 
of  such  an  agent  that  is  thus  preempted  in  advance  ?  Is  it  anything 
and  everything  that  will  make  a  froth  with  a  mineral? 

Much  of  the  phraseology  of  the  Minerals  Separation  patents  is 
vague  and  loose-jointed.  If  intentionally  so,  with  the  idea  of  making 
the  most  favorable  interpretation  in  any  circumstances  that  may  be 
presented,  the  object  is  self-defeated,  for  it  is  an  elementary  principle 
of  legal  interpretation  that  words  shall  be  strictly  interpreted  against 
the  person  using  them. 

This  tendency  is  shown  in  Mr.  Ballantyne's  statement  that  Claim 
No.  1  of  the  Sulman  patent  is  for  the  underlying  idea  of  the  various 
processes,  introducing  by  some  means  or  other  air  under  pressure 
into  pulp  containing  oil  and  water.  "By  some  means  or  other," 
by  any  possible  means,  and  Minerals  Separation  claims  them  all. 
"Agitation  to  form  a  froth"  was  their  great  claim,  and  in  practice 
they  seem  to  claim  any  agitation  for  any  purpose  whatever  and 
any  froth,  however  formed.  So  far  has  this  been  carried  that  it  is 
said  that  Callow  has  desisted  from  the  use  of  a  paddle  to  keep  his 
canvas  clear  from  sand,  although  disclaiming  any  intent  of  forming 
a  froth  with  it,  because  the  Minerals  Separation  company  takes  the 
paddle  to  form  a  froth  and  proposes  to  keep  it  for  all  other  pur- 
poses. 

The  present  situation  of  flotation  metallurgy  is  intolerable. 
There  is  every  appearance  that  some  time,  perhaps  years,  may  pass 
without  a  final  judgment  of  all  the  Minerals  Separation  litigation 
and  meanwhile  they  keep  on  collecting  royalties  from  parts  of  the 
mining  industry  that  are  available  for  coercing  the  rest.  Progress 
is  halted.  Development  is  retarded.  Can  nothing  be  done  to  rid 
the  metallurgical  Sinbad  from  this  Old  Man  of  the  Sea  ?  Statements 


274  THE  FLOTATION  PROCESS 

are  freely  made  that  in  case  of  a  final  Minerals  Separation  victory, 
a  strict  accountability  will  be  required  from  all  infringers. 

The  Norris  process  has  given  excellent  results  with  the  apparatus 
of  both  Minerals  Separation  and  of  Callow,  the  concentrate  being 
of  excellent  grade  from  the  rougher  and  from  a  slower  stirring- 
apparatus  after  the  Elmore  style  of  mixer.  The  process  can  be  adapted 
to  any  type  of  tank,  box,  spitzkasten,  or  other  receptacle  and  there 
is  no  danger  of  defeat  from  an  attack  on  the  Norris  patents  by  the 
Minerals  Separation.  A  method  can  be  devised  to  float  ores  without 
using  the  Minerals  Separation  patents  or  paying  them  royalties. 
The  day  of  royalties  on  daily  tonnage  is  past.  Arrangements  can 
be  made  freeing  the  industry  from  this  toll  and  also  from  extravagant 
prices  for  patented  machinery. 

The  suggestion  has  recently  been  made  that  one  of  the  most 
needed  things  in  the  mineral  industry  at  the  present  time  is  some 
easy  way  of  making  flotation  tests  at  the  mine ;  so  that  a  mill-foreman 
or  mine-boss  may  be  able  to  make  his  tests  on  his  ores  and  decide 
whether  or  not  they  are  susceptible  to  flotation  and  then  design 
a  process  for  treating  them.  Of  course,  any  accomplishments  that 
a  foreman  or  mine-boss  may  have,  add  to  his  value;  and  ability  to 
set  a  broken  leg  or  cure  a  case  of  mountain  fever  might  earn  for 
him  an  additional  salary,  but  aside  from  'first  aid'  to  the  injured, 
no  one  would  want  to  put  himself  in  the  hands  of  the  foreman 
or  the  underground  mine-boss  for  medical  treatment.  It  is  the  same 
way  with  tests  on  flotation.  Aside  from  mere  preliminary  experi- 
ments, testing  ores  for  flotation  is  as  much  a  separately  professional 
matter  as  caring  for  a  broken  leg  or  a  case  of  mountain  fever. 
Metallurgical  engineering  is  now  so  far  advanced  that  there  is  but 
small  reason  for  going  astray  in  the  matter  of  treatment  of  ores 
by  flotation,  provided  adequate  preliminary  tests  are  made  by  expert 
metallurgical  engineers.  The  cost  of  such  tests  is  trifling  and  their 
importance  and  value  not  to  be  exaggerated. 

One  great  reason  why  a  mere  practical  millman  or  miner  cannot 
devise  a  process  from  the  patent  claims  and  specifications  is  that 
most  of  the  important  elements  of  the  actual  installation  are  omitted 
from  the  patent.  The  essential  principle  of  the  patent  of  Elias  Howe 
for  the  sewing  machine  was  that  the  eye  was  in  the  point  of  the 
needle.  Taking  that  for  a  starter,  how  far  would  a  man  get  toward 
building  a  modern  Singer  from  the  Howe  patent?  It  is  like  an 
equation  in  calculus.  Take  such  an  equation  representing  a 
mechanical  movement  and  compare  it  with  another  equation  of  the 


FLOTATION A  PARADOX  275 

path  of  a  comet.  Differentiate  both  and  out  go  the  constant  factors 
and  the  differential  equations  might  be  identical  in  form.  Re-integrate 
them.  Do  you  get  back  your  mechanical  movement  and  your  comet's 
orbit  ?  You  do  not.  Your  constant  factors  do  not  re-appear.  The 
same  way  with  patent  specifications  and  claims.  They  contain  only 
the  differentials.  In  fact,  a  recent  letter  from  the  Patent-Office 
said:  "It  is  suggested  that  the  claims  eliminate  all  unnecessary 
references  to  structure  and  that  they  be  limited  to  the  actual  process 
steps. ' ' 

By  a  proper  combination  of  interests,  not  only  can  there  be 
avoided  the  payment  of  royalties  on  ores  treated  and  high  prices 
for  patented  machinery;  and  not  only  can  every  mill-owner  be 
assured  of  the  constant  high  efficiency  of  his  plant,  but  he  can  be 
protected  against  infringing  patents,  and  if  sued  for  infringement 
he  can  be  defended  at  a  trifling  cost  to  himself,  a  general  fund 
being  provided,  at  a  small  percentage  of  what  the  use  of  the  Minerals 
Separation  patent  would  cost  him.  The  way  to  do  is  to  perfect  a 
process  in  a  metallurgical  laboratory  to  fit  the  special  ore  in  each 
case.  When  the  process  is  perfected  care  must  be  taken  that  it 
includes  the  patent  principle  under  which  it  is  to  be  licensed  and 
does  not  infringe  any  other  patent.  In  one  mine, in  the  Ninth 
Circuit  where  a  home-made  process  has  been  patched  up,  it  seems 
as  though  every  well  known  flotation  patent  has  been  infringed,  and 
yet  the  process  will  not  work  as  it  ought. 

Well,  suppose  the  program  is  carried  out  and  the  Norris  process 
is  generally  adopted,  and  the  Hyde  and  Miami  suits  are  decided 
in  favor  of  the  Minerals  Separation.  That  has  no  effect  on  the 
Norris  process,  not  being  a  party  to  the  present  suits.  A  new  suit 
would  have  to  be  brought  against  new  defendants  and  another  term 
of  years  passed  before  the  Minerals  Separation  could  hope  to  get 
any  money,  however  favorable  their  case.  But  their  case  would  not 
be  favorable.  The  first  thing  that  they  would  meet  would  be  a 
certified  copy  of  the  proceedings  in  their  own  country  where  their 
own  Government  decided  that  the  Norris  process,  although  the 
applicant  was  not  represented  at  the  hearing,  was  not  an  infringe- 
ment of  the  five  patents  governing  the  Froment,  the  Elmore,  or  the 
Minerals  Separation  processes  respectively. 

The  Minerals  Separation  people  were  so  sure  of  their  strategic 
position,  so  confident  that  their  American  patents  would  be  sustained 
by  the  courts  that,  from  what  seems  mere  wantonness,  conditions  were 
imposed  upon  the  licensees  that  were  intolerable;  with  the  result 


276  THE  FLOTATION  PROCESS 


of  a  concerted  movement  on  the  part  of  the  whole  mining  industry 
to  defeat  the  Minerals  Separation  patents  and,  from  the  present 
outlook,  with  every  prospect  of  success. 


FLOTATION   OF   GOLD   ORES. 

(From  the  Mining  and  Scientific  Press  of  December  25,  1915) 
The  Editor: 

Sir — Mr.  A.  E.  Drucker,  well  known  for  his  work  in  cyanidation, 
in  a  letter  appearing  in  your  issue  of  November  20,  made  some  very 
pertinent  remarks  in  regard  to  flotation,  more  particularly  concerning 
its  application  to  gold  and  silver  ores.  His  view  is  that  of  a  metal- 
lurgist rather  than  of  the  man  interested  in  the  introduction  of 
flotation.  There  is,  as  Mr.  Drucker  points  out,  a  place  in  nearly 
every  gold  and  silver  mill  for  a  flotation  plant,  and  from  the  work 
that  I  have  done  so  far,  I  have  come  to  the  same  conclusion, 
namely,  that  flotation  will  be  used  in  connection  with  water  concen- 
tration, and  that  its  best  place  in  a  gold  and  silver  mill  is  in  the 
treatment  of  the  slime. 

I  think  that  in  the  future  a  common  method  for  the  treatment 
of  gold  and  silver  ores  will  be  concentration  by  water  and  the  treat- 
ment of  the  resulting  sand  by  cyanide,  with  the  use  of  flotation  for 
the  slime.  A  scheme  like  this  could  be  adopted  in  many  cases,  thus 
obviating  the  necessity  for  fine  grinding.  The  removal  of  the  pyrite 
from  the  sand  would  allow  quick  treatment  by  cyanidation  of  the 
sand  and  the  flotation  of  the  slime,  which  would  do  away  with  the 
most  expensive  part  of  the  cyanide  plant,  namely,  the  slime  annex. 
However,  the  constantly  recurring  question  would  be:  what  to  do 
with  the  flotation  concentrate.  Considerable  work  is  now  being 
done  in  our  laboratory  to  obtain  a  flotation  concentrate  low  in 
insolubles.  The  average  amount  of  insolubles  is  about  30%.  I  am 
now  carrying  out  some  tests  to  reduce  these  insolubles  to  a  minimum, 
because  if  the  concentrate  is  to  be  handled  or  shipped,  it  should 
contain  the  lowest  possible  percentage  of  insolubles.  Flotation  is 
now  on  the  map  and  will  be  appearing  constantly  in  the  flow-sheets 
of  the  future. 

CHAS.  BUTTERS. 

San  Francisco,  December  13. 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS  277 

TESTING  ORES  FOR  THE  FLOTATION  PROCESS 

By  0.  C.  RALSTON  AND  GLENN  L.  ALLEN 
(From  the  Mining  and  Scientific  Press  of  January  1,  1916) 

INTRODUCTION.  *Although  the  subject  of  testing  for  flotation 
has  been  well  presented  in  T.  J.  Hoover's  book  on  '  Concentrating 
Ores  by  Flotation,'  there  is  need  of  later  information  on  this  timely 
subject.  Much  testing  has  been  done  in  laboratories  not  connected 
in  any  way  with  the  Minerals  Separation  company,  with  which 
Mr.  Hoover  was  formerly  associated  as  metallurgical  engineer,  and 
there  have  been  developed  methods  of  investigation  that  may  prove 
suggestive  to  many  experimenters. 

On  that  account  we  have  compiled  data  on  the  subject  of  testing 
both  from  the  literature  available  and  from  our  own  experience, 
as  well  as  from  what  we  have  seen  in  other  laboratories.  This  paper 
is  designed  to  present  the  results  of  this  compilation,  with  a  critical 
discussion  of  the  more  important  methods  now  in  vogue. 

On  account  of  the  empirical  state  of  the  art  of  flotation  a  great 
deal  of  testing  is  necessary  before  large-scale  practice  can  be 
commenced  on  any  ore;  therefore  a  small  laboratory-machine  is 
necessary  in  which  many  tests  involving  many  variables  can  be  made 
in  a  short  time.  The  machine  must  be  so  designed  and  so  operated 
that  a  close  approximation  to  the  results  possible  with  full-sized 
flotation  machinery  will  be  obtained.  In  a  mill-plant  it  is  a  matter 
of  some  difficulty  to  control  conditions  through  a  wide  range  of 
such  variables  as  temperature,  acidity,  quantity  of  oil,  percentage 
of  solids  in  pulp,  fineness  of  grinding,  etc.,  and  as  the  proper  treat- 
ment of  a  given  ore  can  be  ascertained  only  through  testing  it  first, 
a  critique  of  the  testing  methods  in  use  is  in  order. 

Many  people  have  had  the  experience  of  reading  the  available 
literature  on  flotation-testing  and  of  failing  to  get  satisfactory 
results  when  the  described  testing  was  attempted.  To  actually 
witness  some  good  test-work  and  learn  thereby  the  appearance  of 
froth,  the  exact  manipulation  of  the  machine  and  froth,  goes  far 
toward  bringing  the  beginner  to  a  point  where  he  can  test  efficiently. 


*By  permission  of  the  Director,  U.  S.  Bureau  of  Mines.  Communicated 
by  D.  A.  Lyon,  metallurgist  in  charge  of  the  Salt  Lake  station  of  the  U.  S. 
Bureau  of  Mines,  co-operating  with  the  University  of  Utah.  O.  C.  Ralston, 
^Assistant  Metallurgist  of  U.  S.  Bureau  of  Mines,  and  Glen  L.  Allen,  Research 
Fellow  of  the  University  of  Utah. 


278 


THE   FLOTATION    PROCESS 


None  of  the  literature  mentions  the  fact  that  it  is  difficult  to  get 
a  high  percentage  of  extraction  and  a  high  grade  of  flotation 
concentrate  at  the  same  time.  The  beginner  often  strives  after 
both  of  these  things  in  a  single  test,  whereas  he  should  determine 
how  each  can  be  attained  before  he  attempts  to  obtain  both  simul- 
taneously. Furthermore,  it  is  difficult  to  manipulate  a  small  machine 
to  give  as  good  results  as  a  large  one,  until  after  considerable  practice. 
So  the  small  machine  is  generally  pessimistic,  compared  with  the 
large  one.  It  is  practically  essential  for  the  beginner  to  weigh  and 


-'Feed 


--  -  Concenfrrxfe 


Tailing- 


FIG.    54.       THE    MACQUISTEN    TUBE. 


assay  all  of  his  products  in  order  to  see  if  the  extraction  and  the 
grade  of  concentrate  are  satisfactory,  where  an  experienced  manipu- 
lator can  often  tell  by  aid  of  past  experience  and  the  use  of  a  glass 
or  microscope  whether  he  is  getting  good  results  or  not. 

With  these  points  in  view,  we  shall  describe  first  the  satisfactory 
machines  and  their  operation.  Then  we  shall  give  a  more  general 
exposition  on  what  variables  to  Study  and  what  points  to  observe. 

Flotation  test-apparatus  must  necessarily  be  classified  in  the  same 
way  as  large-scale  machines,  namely,  as  film-flotation  machines,  acid- 
flotation  machines,  and  froth-machines  of  both  pneumatic  ancj 
mechanically  agitated  types.  Film-flotation,  as  exemplified  in  the 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS  279 

Macquisten1  and  in  the  Wood  machines,  does  not  seem  to  have 
the  same  wide  application  as  does  froth-flotation;  hence  little  need 
be  said  about  them. 

FILM-FLOTATION.  Macquisten  tubes  have  such  small  capacity  that 
a  single  tube  is  small  enough  for  test-work  on  a  few  pounds  of  ore 
at  a  time  (see  Fig.  54).  A  small  4-ft.  tube  is  known  to  give  trust- 
worthy results,  although  a  longer  one  is  more  desirable.  Testing 
with  a  Macquisten  tube  was  done  for  several  years  in  the  laboratory 
of  the  General  Engineering  Co.,  of  Salt  Lake  City,  of  which  company 
J.  M.  Callow  is  president.  Since  Mr.  Callow  has  begun  the  exploita- 
tion of  his  own  pneumatic  frothing-machine  this  work  has  been  set 
aside. 

The  Wood  machine  can  be  built  in  miniature  and  for  several 
years  a  small  machine  of  the  type  sketched  has  been  used  in  the 
plant  of  the  Wood  ore-testing  works  at  Denver.2  This  small  machine 
was  about  two  feet  long  and  one  foot  wide.  The  method  of  operation 
is  the  same  as  that  of  the  full-sized  machine.  (See  Fig.  55.) 

As  neither  of  these  machines  has  been  much  used  in  practice, 
they  are  merely  mentioned  for  the  sake  of  completeness.  Hoover3 
has  recommended  a  test  on  a  vanning-plaque,  so  that  the  sulphides 
will  float  off  onto  the  surface  of  the  water,  but  we  consider  this 
test  of  practically  no  value.  Hoover,  however,  acknowledges  that 
it  is  merely  a  test  illustrative  of  the  film  processes. 

In  testing  ores  for  the  Potter  or  the  Delprat  processes,  Hoover's 
text  is  again  the  source  of  information.  An  illustrative  test-tube 
experiment  is  pictured  in  Fig.  56.  Tubes  containing  3%  H2S04  or  acid 
salt-cake  solutions  and  a  little  sulphide  ore  are  warmed  nearly  to  the 
boiling  temperature.  Bubbles  of  C02  attach  themselves  to  the  sul- 
phides, travel  to  the  surface  of  the  solution,  discharge  into  the  air,  and 
drop  the  sulphides  into  the  pocket  on  the  under  side  of  the  tube,  as 
shown  in  the  annexed  sketch.  In  another  test  a  200-c.c.  beaker  is 
used  with  100  c.c.  of  3%  H2S04  and  brought  to  nearly  boiling 
temperature.  The  ore  when  introduced  into  this  yields  a  froth 
composed  of  sulphides  supported  by  bubbles  of  C02.  In  case  the 
ore  is  deficient  in  carbonate,  an  addition  of  as  much  as  3%  of  calcite 
or  siderite  is  made.  The  froth  is  skimmed  with  a  spoon  as  soon  as 
it  forms.  We  have  noticed  that  a  great  deal  of  mineral  is  often 
lifted  partly  but  never  reaches  the  surface.  Consequently  extractions 


^Mining  and  Scientific  Press,  Vol.  XCVI,  page  414  (1908). 

2H.  E.  Wood.    Trans.  A.  I.  M.  E.,  Vol.  XLIV,  pp.  684-701  (1912). 

sT.  J.  Hoover.    'Concentrating  Ores  by  Flotation,'  1st  edition,  page  77. 


280 


THE   FLOTATION   PROCESS 


are  low,  although  the  grade  of  concentrate  obtained  is  often  very 
good.  For  practical  purposes,  however,  the  test  is  not  of  much 
value.  A  better  test-machine  is  the  small  unit  shown  in  Fig.  57.  The 
acid  should  be  allowed  to  run  down  through  a  section  of  garden- 
hose  to  within  an  inch  of  the  surface  of  the  ore  and  the  ore  should 


PlG.   55.      THE  WOOD   MACHINE. 

be  kept  stirred  with  a  wooden  paddle  so  that  the  bubbles  of  C02 
generated  by  the  action  of  the  acid  can  lift  the  sulphides  out  of 
the  body  of  the  pulp.  The  froth  formed  should  be  skimmed  with 
the  paddle  as  fast  as  made,  then  filtered,  dried,  weighed,  and  analyzed. 
Not  many  ores  yield  gracefully  to  this  treatment  and  slimes  give 
poor  extractions.  Fines  and  Wilfley-table  middlings  are  better 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS 


281 


adapted,  and  the  presence  of  siderite  in  the  pulp  is  desirable,  as  it 
reacts  slowly  with  dilute  acid.  From  1  to  3%  H2S04  is  best  in 
testing  and  |  to  1|%  solutions  on  the  large  scale  will  give  about  the 
same  results.  The  temperature  of  the  pulp  should  be  maintained 
at  70°  C.  by  use  of  a  steam  jet.  Five  to  ten  pounds  of  ore  per  test 
is  necessary.  The  extractions  obtained  are  always  lower  than  in 
full-sized  units.  While  oil  is  not  necessary  in  this  process,  it  will 
greatly  assist  in  the  flotation,  and  the  addition  of  a  small  amount  is 
often  of  much  assistance  in  test-work. 

MECHANICAL  FROTHING  as  developed  by  the  Minerals  Separation 
company  in  England  and  Australia,  and  modified  by  many  others, 
has  been  one  of  the  most  important  methods  of  flotation.  Therefore 


FIG.   56.      TEST-TUBES  FOE  FLOTATION. 


the  laboratory  machinery  that  has  been  developed  is  at  as  high  a 
state  of  perfection  as  any  such  machinery  now  in  use. 

The  Janney  machine  is  probably  the  best  designed  machine  for 
getting  reliable  quantitative  results  on  a  small  quantity  of  ore. 
Photographs  and  sketches  are  appended  (Fig.  58,  59,  and  60).  It  can 
be  seen  that  the  agitation  compartment  is  cylindrical  in  shape  and 
that  its  top  is  surrounded  by  a  froth-box,  which  slopes  into  a  spitz- 
kasten,  where  the  froth  can  be  skimmed.  The  tailing  sinks  to  a 
return-hole  at  the  bottom,  passing  into  the  agitation-compartment 
again.  To  provide  good  agitation,  four  vertical  baffles  are  attached 
to  the  wall  of  the  agitation-compartment,  against  which  the  pulp  is 
swirled  by  the  two  impellers.  Lining  the  walls  with  expanded  metal 
lathing  or  with  a  coarse-mesh  iron  screen  adds  to  the  thorough  mixing 
that  the  pulp  must  receive.  The  two  impellers  are  on  a  common 


282 


THE   FLOTATION    PROCESS 


shafting,  which  enters  the  machine  through  a  stuffing-box  in  the 
bottom  of  the  machine.  The  lower  impeller  with  four  vertical  vanes 
is  submerged;  it  agitates  and  emulsifies  the  pulp  while  the  upper 
impeller,  likewise  with  four  vertical  vanes,  acts  as  a  pump  to  lift 
the  pulp  and  beat  air  into  it.  A  pulley  and  belt  connects  the 
shafting  with  a  variable-speed  motor. 

A  dome-shaped  lid  is  used  on  the  machine.  A  small  hole  in  the 
top  of  the  dome  allows  the  introduction  of  oil,  acid,  water,  or 
other  materials  without  the  removal  of  the  lid.  The  lid  is  so 
constructed  that  it  can  be  turned  upside-down  with  the  dome 


L/r?e. 


Garden  Hose. 

(Wooden  Padd/e. 


FlG.    57.      A  POTTEB-DELPBAT   TEST. 

extending  down  into  the  froth-box,  and  in  this  position  it  can  act 
as  a  funnel.  The  dome  rests  then  on  the  top  of  the  agitation- 
compartment  and  no  froth  can  escape  into  the  froth-box.  This 
allows  a  period  of  agitation  of  the  pulp  before  the  dome-top  is 
turned  right-side  up  to  allow  aerated  pulp  to  overflow  into  the  froth- 
box  and  down  into  the  spitzkasten,  where  the  froth  can  be  removed. 

A  discharge-plug  at  the  bottom  of  the  machine  allows  the  flushing 
out  of  tailing  after  the  test  has  been  completed.  So  careful  has 
been  the  design  of  this  test-machine  that  even  this  discharge-plug 
is  beveled  to  fit  flush  with  the  bottom  of  the  machine  and  thus  afford 
no  dead  space  in  which  the  solids  might  settle. 

The  spitzkasten  is  long  and  narrow,  in  order  to  permit  a  deep 
froth  to  be  formed  and  to  travel  over  as  long  a  space  as  possible, 
before  reaching  the  discharge.  This  tends  to  allow  more  of  the 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS 


283 


entrained  gangue  to  settle  out  of  the  mineral  froth.  The  sides  of 
the  spitzkasten  are  of  heavy  plate-glass,  each  fastened  to  a  metal 
frame  by  means  of  screws.  The  wrought-iron  shaft  projects  through 
a  brass  stuffing-box  and  is  supported  by  a  ball-bearing  beneath.  All 
the  other  metal  parts  are  of  cast  aluminum. 

The  small  variable-speed  motor  may  be  of  either  D.  C.  or  A.  C. 


FIG.   58.      THE  JANNEY  MACHINE.      COVER  INVERTED. 


type.  F.  G.  Janney  recommends  the  use  of  a  General  Electric, 
shunt-wound,  direct-current  motor,  for  230  volts,  with  a  rated  speed 
of  1700  r.p.m.  and  J  hp.  The  impeller-shaft  is  to  be  driven  at  1900 
r.p.m.  maximum  speed.  For  speed-control  he  recommends  a  General 


284  THE  FLOTATION  PROCESS 

Electric   direct-current   field-rheostat,   with   an   ampere   capacity   of 
1.25  to  0.063  at  250  volts. 

In  our  own  laboratory  it  was  desirable  to  use  the  ordinary  city- 
lighting  circuit  of  110  volts,  A.  C.     On  that  account  we  have  found 


FlG.   59.      THE  JANNEY  MACHINE.      COVER  UPRIGHT. 

the  following  motor  satisfactory:  J-hp.  General  Electric  repulsion 
induction  motor,  single-phase,  60-cycle,  with  full  speed  of  1780  and 
carrying  4.2  amperes  at  110  volts,  or  2.1  amperes  at  220  volts, 
depending  upon  the  voltage  of  the  current  supplied  to  the  machine, 
either  voltage  being  acceptable.  Speed-control  is  obtained  by  the 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS 


285 


use  of  an  ordinary  field-rheostat  in  series  with  the  motor.  Such  a 
motor  has  a  speed  varying  with  the  load  and  with  the  voltage 
applied.  As  the  load  is  practically  a  constant,  the  speed  will  depend 
upon  the  amount  of  resistance  in  series  with  the  motor.  As  the 
majority  of  laboratories  find  a  city  alternating  current  more  con- 
venient to  obtain,  such  a  motor  is  recommended. 

The  operation  of  the  machine  is  as  follows:    It  is  set  up  on  a 
bench  convenient  to  the  sink  and  to  running  water.     The  motor  is 


Concentrate 

Filter  Cone. 


FlG.    60.      THE  JANNEY  TEST   MACHINE. 

set  up  one  foot  to  the  rear  with  the  switch  and  rheostat  placed  so 
that  they  can  be  easily  reached  while  standing  in  front  of  the 
machine.  A  ^-in.  round-leather  sewing-machine  belt  is  used  for 
drive.  The  bearings  are  well  oiled,  the  stuffing-box  is  properly 
packed,  and  some  attention  should  be  given  to  it  occasionally  in 
order  to  see  that  it  is  kept  screwed  tight  enough  to  avoid  leakage. 

Enough  clear  water  is  run  into  the  machine  to  barely  show  in 
the  spitzkasten  and  the  motor  is  started  at  its  lowest  speed.  A 
500-gm.  charge  of  ore  ground  to  at  least  48-mesh  is  added  and  the 
cover  placed  on  the  machine  in  its  inverted  position.  (See  Fig.  58.) 
This  is  done  to  allow  thorough  mixing  without  circulation  of  the 
pulp.  All  or  part  of  the  oil  and  other  reagents  are  now  added 


286  THE  FLOTATION  PROCESS 

and  the  motor  brought  up  to  full  speed  for  30  seconds.  The  speed 
is  again  lowered  to  the  minimum  and  the  cover  is  turned  over  into 
its  upright  position.  (See  Fig.  59.)  The  speed  is  then  raised  and 
water  is  added  through  the  hole  in  the  top  of  the  lid  until  the  froth 
in  the  spitzkasten  is  nearly  at  the  overflow  lip.  The  ultimate  speed 
of  the  agitator  will  depend  somewhat  upon  the  character  of  this 
froth,  as  some  oils  will  give  a  deep  persistent  froth,  while  other 
froths  are  thin  and  brittle  and  allow  of  more  water  being  added 
to  the  machine,  as  well  as  more  violent  agitation  in  order  to  beat 
more  air  into  the  pulp.  The  froth  may  either  be  allowed  to  flow 
out  of  the  spitzkasten  of  its  own  weight  or  skimmed  with  a  small 
wooden  paddle.  It  is  a  good  idea  to  wet  the  glass  sides  of  the  ' spitz' 
with  water  while  the  froth  is  rising,  so  that  none  of  the  froth  will 
stick  to  the  glass.  .  ^ 

The  duration  of  the  test  is  about  five  minutes  with  an  ore  that 
floats  easily,  while  other  ores  will  require  a  considerably  longer  time 
to  allow  the  entrained  gangue  to  settle  out  of  the  froth  before  it  is 
discharged  from  the  machine.  In  such  cases  it  is  best  to  hold  back 
the  froth  until  its  appearance  shows  it  to  be  fairly  clean.  Beginners 
are  likely  to  dilute  their  froth  with  too  much  gangue.  In  a  large- 
sized  machine  the  froth  can  travel  over  from  four  to  eight  feet  of 
spitzkasten  before  it  is  discharged,  while  in  this  test-machine  it 
only  has  a  travel  of  about  10  inches.  Consequently,  the  small 
machine  is  liable  to  yield  concentrate  of  too  low  a  tenor.  The  same 
applies  to  most  other  machines  for  making  tests  on  flotation. 

The  concentrate  may  be  caught  in  a  pan  or  on  a  filter.  After 
the  test  the  machine  is  brought  back  to  low  speed  and  the  tailing- 
plug  removed,  so  that  the  tailing  can  be  caught  in  a  pan  or  bucket, 
or  run  to  waste. 

If  it  is  so  desired,  this  rough  concentrate  can  be  put  back  into 
the  machine  and  treated  in  the  same  way  as  the  original  sample, 
or  the  concentrates  from  several  tests  combined  to  give  enough  material 
for  re-treatment.  If  this  is  done  three  products  are  made,  namely : 

A  'rougher'  tailing,  to  waste. 

A  clean  concentrate,  for  shipment. 

A  'cleaner'  tailing  or  middling,  which  in  actual  practice  is 
returned  to  the  head  machine. 

When  these  conditions  are  observed  results  only  slightly  lower 
than  those  possible  with  a  big  machine  can  be  obtained.  A  test  can 
be  run  in  from  5  to  30  minutes  in  such  a  machine  with  500  grams 
of  ore  in  anything  from  a  3 : 1  to  a  5 : 1  pulp.  The  glass  sides  of 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS 


287 


the  spitzkasten  allow  close  observation  of  the  condition  of  the  froth, 
and  this  is  a  great  advantage  to  the  beginner.  The  small  amount  of 
ore  necessary  for  a  test  is  a  matter  of  considerable  convenience  as 
fine  grinding  of  the  ore  in  the  laboratory  is  often  irksome.  The 
aluminum  casting  is  little  corroded  by  either  acid  or  alkaline 
electrolytes.  The  return  of  pulp  from  the  'spitz'  to  the  agitating- 


Concentrate. 


Trough  for  Froth. 


'Contracted  Spifzkas-f-en. 


FIG.    61.       SKETCH   OF  THE  LYSTER  OB  HOOVER   MACHINE. 


FIG.    62.      ANOTHER   FORM    OF    HOOVER    MACHINE. 

compartment  allows  the  material  to  be  treated  until  all  mineral  has 
been  removed  without  stopping  the  machine,  so  that  a  single  treat- 
ment yields  a  clean  tailing.  However,  a  second  treatment  of  this 
'rougher-froth'  is  sometimes  necessary  in  order  to  get  a  high-grade 
concentrate.  Clean  tailings  generally  mean  only  medium-grade 


288  THE  FLOTATION  PROCESS 

concentrates  due  to  entrainment  of  gangue,  in  the  removal  of  all 
the  mineral. 

The  stuffing-box  in  the  bottom  will  probably  leak  if  not  watched. 
However,  this  driving  of  the  impellers  from  below,  instead  of  from 


FIG.    63.       THE    HOOVER    MACHINE. 


above,  leaves  the  top  of  the  machine  free  for  the  operator  and  is 
more  convenient  in  every  way.  This  is  of  importance  in  a  laboratory- 
machine,  and  will  excuse  the  use  of  a  stuffing-box.  In  large-scale 
machines  a  stuffing-box  underneath  would  not  be  tolerated,  and  the 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS 


289 


drive  should  be  from  above.  We  would  also  suggest  a  sheet-lead 
construction  as  being  more  easily  built.  A  J-inch  sheet-lead  is 
sufficiently  rigid  to  stand  up  well,  while  it  is  ductile  enough  to  be 


FIG.    64.  THE    HOOVER    MACHINE,    SHOWING    STIRRER. 

A.  Spitzkasten. 

B.  Agitation  compartment. 

C.  Variable-speed  motor. 

D.  Retaining  bolts. 

E.  Impeller. 

F.  Concentrate  discharge. 


290  THE  FLOTATION  PROCESS 

worked  readily  into  the  desired  shape.  The  joints  are  easily  burned, 
and  it  is  acid-proof. 

THE  HOOVER  MACHINE,  so-called,  was  designed  after  a  test- 
machine  described  in  the  second  edition  of  Hoover's  book,  being 
copied  from  one  of  Lyster's  patents,  and  has  been  much  copied  by 
people  wishing  to  make  flotation  tests.  An  improvement  over  this 
construction  was  published  by  Ralph  Smith4  recently  (see  Fig.  61), 
and  a  modified  sketch  of  the  same  is  shown  in  Fig.  62,  while 
photographs  of  the  machine  used  for  a  while  in  our  laboratory  are 
shown  in  Fig.  63  and  64.  Either  a  variable-speed  motor  is  belted  to 
the  pulley  that  drives  the  stirring  mechanism,  or  a  pair  of  cone- 
pulleys  on  a  constant-speed  motor  is  used.  This  construction  has 
been  popular  because  it  can  be  made  of  wood,  at  small  expense. 
The  Janney  machine  will  cost  about  $100,  while  the  Hoover  machine 
can  be  built  for  a  small  fraction  of  that  amount.  Mr.  Hoover's 
original  drawing  does  not  show  the  spitzkasten  drawn  to  a  point, 
as  only  the  front  side  was  beveled.  Our  sketch  shows  both  sides 
beveled.  This  is  desirable,  as  it  eliminates  space  in  which  fine 
sand  can  settle,  and  tends  to  minimize  the  amount  of  pulp  lying 
inactive  in  the  spitzkasten.  In  the  agitation-compartment  the  pulp 
is  swirled  into  the  corners,  where  it  is  well  mixed  with  air;  hence 
the  baffles  sketched  in  the  Janney  machine  are  unnecessary.  One 
objection,  however,  is  that  unless  the  agitation-compartment  is  very 
tall  the  pulp  being  swirled  into  the  corners  has  a  tendency  to 
splash  out,  and  a  lid  similar  to  the  one  on  the  Janney  machine  is 
desirable.  However,  it  is  difficult  to  attach  one  because  the  stirrer- 
shafting  is  in  the  way.  The  operation  of  this  machine  is  practically 
the  same  as  that  of  the  Janney,  except  that  without  glass  sides  on 
the  spitzkasten  it  is  hard  to  get  as  clean  a  froth.  A  charge  of  1000 
to  SOOO  grams  is  necessary  in  this  machine. 

THE  SLIDE  MACHINE,  as  shown  in  Fig.  65  and  66,  was  designed 
by  Hoover  and  perfected  by  many  others.  In  recent  practice  it  is 
motor-driven.  A  number  of  these  machines  were  given  by  James  M. 
Hyde  to  various  universities  in  this  country.  Many  people  favor 
this  apparatus  for  the  reason  that  they  have  had  little  opportunity 
to  use  any  other  design.  In  this  machine  the  agitator  is  driven 
from  below  through  a  stuffing-box,  as  in  the  Janney,  with  the 
consequent  freedom  of  the  top  of  the  machine  for  the  convenience 
of  the  operator.  The  top  half  of  the  machine  is  so  constructed  that 
it  can  be  slid  to  one  side,  cutting  off  the  froth  formed  in  the  agitation 

*E.  &  M.  J.,  Vol.  C,  page  395  (1915). 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS 


291 


from  the  gangue,  which  is  allowed  to  settle.  The  operation  consists 
in  agitating  with  oil  and  other  reagents,  then  a  period  of  quiet 
during  which  the  froth  collects  at  the  top  while  the  gangue  sinks. 
Two  windows  in  the  side  enable  the  observer  to  see  when  the  gangue 
has  subsided  sufficiently  to  allow  the  top  half  to  be  slid  along  the 
rubber  gasket,  cutting  off  the  froth  from  the  remainder  of  the 
pulp.  The  time  necessary  for  the  settling  of  the  gangue  is  sufficient 
for  much  of  the  gangue  to  separate  from  the  froth,  leaving  only 
clean  sulphides  in  the  froth.  This  element  of  the  machine  has 
made  it  of  some  value  in  testing  flotation  oils,  but  in  a  weak  froth 


FlG.    65.      THE    SLIDE   MACHINE. 

much  of  the  sulphide  mineral  also  settles  out  and  is  lost,  so  that 
the  test  results  with  this  machine  often  show  unnecessarily  low 
extractions  and  a  high  grade  of  concentrate.  On  the  other  hand, 
when  conditions  are  adjusted  to  give  a  froth  persistent  enough  to 
hold  all  the  sulphide  mineral,  considerable  gangue  is  entrained  in 
the  stiff  froth.  Further,  after  skimming  one  froth  we  find  it  neces- 
sary to  add  more  water  and  start  the  machine  again  to  make  more 
froth.  It  is  hard  to  make  the  slide  machine  give  a  high  extraction 
with  only  one  agitation.  The  intermittent  character  of  such  work 
and  the  time  necessary  to  wait  while  settling  are  disadvantages  that 
make  the  Janney  or  the  Hoover  machines  of  greater  utility,  in  our 
opinion.  The  parts  are  of  cast  aluminum  with  a  rubber  gasket 
between.  A  charge  of  500  to  1000  grams  of  ore  is  used. 

As  regards  the  fineness  of  crushing  in  laboratory  work,  material 
ground  as  fine  as  200-mesh  will  yield  high  extractions  with  much 


292 


THE   FLOTATION    PROCESS 


LONGITUDINAL   SECTION. 

FIG.    66.      THE    SLIDE    MACHINE. 

A.  Upper  part  of  cell. 
(7.     Lower  part. 

B.  Rubber  cushion. 

D.  Tail  to  prevent  leakage  of  froth. 

E.  Agitator. 

F.  Hole  for  withdrawal  of  tailing. 

greater  ease  than  coarser  material.  It  is  possible  to  get  acceptable 
work  in  some  cases  with  material  as  coarse  as  40-mesh  on  condition 
that  there  is  a  considerable  portion  of  the  same  material  in  the  slime. 
For  ordinary  laboratory  work  a  convenient  size  is  80-mesh,  unless  poor 
extractions  are  obtained. 

[The  General  Engineering  Co.  at  Salt  Lake  City  and  the  Mine 
&  Smelter  Supply  Co.,  at  Denver,  sell  flotation  machines.  So  does 
the  Denver  Fire  Clay  Co.,  which  makes  a  modified  Hoover  machine. 
The  Joshua  Hendy  Iron  Works,  San  Francisco,  makes  machines  for 
the  Minerals  Separation  company. — EDITOR.] 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS II 


293 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS— II 

By  0.  C.  RALSTON  and  GLENN  L.  ALLEN 
(From  the  Mining  and  Scientific  Press  of  January  8,  1916) 

SEPARATORY  FUNNELS.  During  the  past  year  an  article  on  practice 
in  Mexico5  mentioned  the  fact  that  much  of  the  preliminary  testing 
on  the  ore  was  done  in  separatory  funnels,  in  which  the  charges  of 
pulp,  oil,  etc.,  were  shaken,  after  which  the  cock  at  the  bottom  of 


FlG.    67.       SEPARATING   FUNNEL. 

the  funnel  was  opened  and  the  tailing  run  into  a  second  separatory 
funnel  for  further  flotation  tests,  the  cock  being  closed  in  time  to 
catch  the  froth.  The  versatility  of  experiment  permissible  with 
the  use  of  such  apparatus  (Fig.  67)  is  commendable.  Obviously, 
this  arrangement  is  open  to  the  same  objections  as  is  the  slide 


&M.  &  8.  P.,  Vol.  CXI,  page  122  (July  24,  1915). 


294  THE  FLOTATION  PROCESS 

machine  except  that  separatory  funnels  are  simple  and  inexpensive. 

ELMORE  MACHINE.  As  far  as  we  know,  no  small  test-machine 
for  the  Elmore  process  has  come  into  common  use  on  account  of 
the  fact  that  the  pulp  must  be  lifted  through  a  tube  corresponding 
in  length  to  the  column  of  water  equivalent  to  barometric  pressure. 
This  makes  an  awkward  laboratory  machine.  Mr.  Hoover  (2nd 
edition,  page  98),  describes  "illustrative"  experiments  with  the  pulp 
in  a  bottle  connected  with  a  water-pump  for  producing  a  vacuum, 
but  no  quantitative  method  of  this  kind  has  been  developed. 

Other  miscellaneous  frothing  tests  are  in  the  literature  but  most 
of  them  are  merely  "  illustrative. "  Putting  a  charge  into  a  soda- 
water  siphon,  pumping  in  air  to  dissolve  the  water,  and  then  releasing 
the  charge  into  a  beaker  gives  nice-looking  froth.  In  some  of  the 
lawsuits  square  glass  candy  jars  (Fig.  68)  with  a  motor-driven 
impeller  have  been  used  to  show  flotation  phenomena  in  court.  In  a 
recent  U.  S.  Patent  (No.  1,155,836)  taken  out  by  T.  M.  Owen,  one 
of  the  engineers  of  the  Minerals  Separation  company,  is  a  sketch  of  a 
simple  test-machine  made  of  an  ordinary  2J-litre  acid-bottle.  (See 
Fig.  69.)  This  corresponds  to  the  sub-aeration  type  of  machine 
and  is  recommended  by  Mr.  Owen  for  test-work  when  such  a  type 
of  machine  seems  necessary,  as  in  differential  flotation.  Air  is  led 
into  the  pulp  through  the  stopper  in  the  bottom  and  beaten  into 
the  pulp  by  the  impeller.  The  four  large  baffles  above  the  impeller 
prevent  the  swirling  of  the  pulp  from-  rising  through  them,  so  that 
there  is  a  quiet  zone  in  the  top  of  the  machine  where  the  froth 
can  collect.  One  great  beauty  of  such  a  machine  is  that  any  froth 
formed  will  rise  immediately  to  the  discharge.  However,  we  believe 
that  the  Janney  and  Hoover  machines  are  the  most  useful  of  the 
mechanically-agitated  type. 

PNEUMATIC  FLOTATION.  Among  the  different  pneumatic  machines, 
as  far  as  we  are  acquainted,  the  Callow  test-machine  is  the  only  one 
of  laboratory  size  that  has  been  much  developed.  It  is  merely  the 
commercial  Callow  machine  reduced  in  size  (see  Fig.  70,  71,  and  72). 
Later  development  in  the  laboratory  of  the  General  Engineering  Co., 
in  Salt  Lake  City,  has  resulted  in  the  reproduction  of  the  whole 
plant  in  miniature  (as  shown  in  Fig.  72),  with  a  Pachuca  mixer,,  a 
roughing-cell,  cleaning-cell,  vacuum-filter,  and  sand-pump  to  return 
middling  to  the  Pachuca  mixer.  As  seen  in  the  drawing,  the  pulp 
is  mixed  well  in  a  Pachuca  tank  of  small  size,  overflowing  into  the 
rougher  flotation-cell.  The  tailing  from  this  rougher  goes  to  a  sand- 
pump  and  is  returned  to  the  Pachuca.  The  froth  is  treated  in  a 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS — II 


295 


AIK  CONNECTION 


Pu  L  L  E  Y5_r 


UPPORT 


o 


ROTATING 
HOLLOW  SHAFT 

TO  ADMIT  AlR 


HOLES 

FlG.  68.    THE  SQUARE  GLASS  JAB  MACHINE  FOB  MAKING  FLOTATION  TESTS. 


296 


THE   FLOTATION   PROCESS 


second  and  smaller  pneumatic-flotation  unit,  giving  a  concentrate 
that  overflows  into  an  ordinary  laboratory  vacuum-filter  actuated 
by  a  water  or  aspirating  pump.  The  tailing  from  the  'cleaner-cell' 
consists  of  a  middling  that  likewise  flows  to  the  sand-pump  and 
back  to  the  Pachuca. 


Fir/ley. 


-Glass  Jar. 


-4Baffles. 


Impeller. 


Woocfen  Cork. 
—  Pipe  Nipple. 
Check  Valve. 

/•d/r  Inlet. 


FlG.    69.      OWEN   TEST-MACHINE. 

A  novice  will  have  no  small  difficulty  in  operating  such  an 
installation,  as  there  are  a  number  of  things  to  be  kept  in  operation 
at  the  same  time.  The  mixture  of  ore,  water,  oil,  and  any  other 
reagents  is  fed  either  into  the  suction  of  the  sand-pump  or  into  the  top 
of  the  Pachuca  after  air  has  been  started  into  the  various  machines. 
The  overflow  from  the  Pachuca  into  the  rougher-cell  accumulates 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS — II 


297 


until  a  nice  froth  is  coming  up  and  nearly  overflowing.  Then  the 
tailing-discharge  valve  on  the  rougher  is  gradually  opened  and  froth 
allowed  to  overflow  from  the  cell  into  the  'cleaner '-cell.  It  is  best 
to  get  most  of  the  charge  circulating  before  much  concentrate^froth 


B 


FlG.   70.      THE  CALLOW  CELL    (EARLY   FORM). 

A.  Froth-overflow  launders. 

B.  Pulp-feed  to  air-blankets. 

C.  Air-atomizing  blanket. 

D.  Concentrate  discharge. 

E.  Compressed-air  feed  to  wind-boxes. 


298 


THE   FLOTATION   PROCESS 


is  allowed  to  overflow,  the  overflow  of  froth  being  controlled  by 
the  main  air-valves  leading  to  each  unit.  After  the  valves  into 
the  individual  wind-boxes  beneath  the  machine  have  been  once 
adjusted  they  should  never  be  disturbed,  and  all  control  of  air 
supplied  should  be  at  the  valves  in  the  main  pipes.  When  every- 
thing is  going  well,  the  air-pressure  in  the  cleaner  can  be  increased 
until  concentrate-froth  is  overflowing  into  the  vacuum-filter.  A 
wooden  paddle  to  stir  any  settled  material  in  the  flotation  cells  is 
of  value,  as  well  as  a  small  jet  of  water  from  a  rubber  hose  for 
washing  concentrate  along  the  froth-launders  and  for  beating  down 
froth  when  occasional  too-violent  rushes  of  froth  from  the  cells  take 
place.  After  a  test  is  complete  the  pulp  should  be  drained  completely 
from  all  parts  of  the  machine  while  the  air  is  still  blowing,  so  that 


Air  L  me,4  /te Pressure . 

Pressure  Gauge 
Tailing  from/tougher 
anct 'C/eaner CeJ/s- 


FIG.   71.      CALLOW  TEST  SET. 

solids  will  not  settle  in  passages  or  clog  the  canvas  blanket  in  the 
cells.  Only  practice  will  allow  anyone  to  get  reliable  results  with 
this  machine.  A  watch-glass  for  catching  and  panning  occasional 
samples  of  froth  is  another  necessary  auxiliary  to  this  equipment. 
The  cost  of  installing  such  a  set  of  apparatus  is  from  $100  to  $150. 
At  least  1000  grams  of  ore  is  required  for  a  test  and  about  30  minutes 
to  1  hour  is  spent.  It  can  be  seen  that  nothing  but  a  finished  concen- 
trate and  a  tailing  are  obtained  or  a  middling  product  may  be  left  in 
the  cleaner  cell.  This  middling  may  be  assayed  as  such  and  calculated 
into  the  concentrate  and  tailing  or  its  sulphides  may  be  panned  out 
and  added  to  the  concentrate.  The  machine  is  said  to  give  results 
closely  paralleling  those  obtained  with  larger-scale  apparatus.  A 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS — II  299 

source  of  supply  of  compressed  air  at  3  to  5  Ib.  per  sq.  in.  is  necessary 
and  the  main  valves  on  the  air-pipe  leading  to  each  machine  should 
be  some  type  of  needle-valve  in  order  to  ensure  exact  control. 

In  testing  practice,  the  air-lift  type  of  middling-return  has  been 
found  more  satisfactory  than  the  centrifugal  pump  shown  in  Fig.  71. 

LABORATORY  MANIPULATIONS.  Turning  from  the  description  of  the 
machines  used  to  the  operations  on  the  ore  before  and  after  the 


FlG.   72.      CALLOW  TEST-MACHINE  WITH  PACHUCA   MIXER. 

A.  Pachuca  mixer. 

B.  Pulp-feed  to  air-blanket. 

C.  Needle-valve  air-control. 

D.  Blanket-clamps  for  quickly  removing  blanket 

for  cleaning. 

E.  Wind-boxes. 

flotation  operation,  we  have  in  general  the   problems  of  crushing 
the  ore  and  of  drying  the  froth-concentrate. 

As  a  rule  laboratory  machinery  for  the  pulverization  of  ore  is 
of  the  dry-grinding  type,  with  the  exception  of  small  ball-mills  that 
can  crush  from  1  to  100  Ib.  charges  in  the  wet.  Consequently,  most 


300  THE  FLOTATION  PROCESS 

people  start  with  weighed  charges  of  finely-ground  dry  ore,  a  known 
quantity  of  water,  of  oil,  and  of  acid  or  alkali.  Our  experience  has 
been  that  most  dry-ground  ore  must  be  treated  in  an  acidified  pulp 
to  get  good  flotation.  Doubtless  the  surfaces  of  sulphide  particles 
become  somewhat  oxidized  in,  or  shortly  after,  dry  grinding  and 
the  function  of  the  acid  would  be  to  clean  the  slightly  oxidized 
surfaces.  Wet  grinding  usually  does  not  call  for  so  much  acid.  In 
nearly  all  laboratory  work  finer  grinding  than  is  used  in  practice 
seems  to  be  necessary.  This  may  possibly  be  due  to  the  smaller 
amounts  of  froth  that  are  formed.  Such  small  quantities  of  froth 
cannot  form  layers  as  deep  as  those  made  in  the  large  machines. 
If  a  big  particle  of  sulphide  can  be  entrained  with  a  number  of 
smaller  particles,  it  can  be  floated,  but  with  a  thin  froth  the  chance 
of  such  entrainment  would  seem  to  be  less.  Some  experimenters 
have  informed  us  that  they '  were  able  to  float  even  as  large  as 
30-mesh  material,  but  our  own  experience  is  that  60-mesh  material 
is  often  hard  to  float  with  any  chance  of  getting  a  high  extraction, 
while  the  operation  is  performed  with  much  more  ease  and  expedition 
when  the  ore  is  crushed  somewhat  finer. 

Wet  grinding  is  more  desirable,  as  it  parallels  conditions  in 
practice,  where  most  of  the  finer  grinding  of  ore  is  in  Chilean,  tube, 
and  other  mills.  However,  wet  grinding  is  harder  to  manipulate 
in  a  small  laboratory  and  requires  more  time.  The  dry  weight  of 
the  feed  to  the  flotation  machine  must  be  known;  hence  a  weighed 
charge  of  dry  ore  crushed  to  about  10-mesh  can  be  introduced  into 
a  porcelain  or  iron  pebble-mill  for  grinding  and  ground  for  the 
length  of  time  found  necessary  to  reduce  the  pulp  to  sufficient  fine- 
ness— 15  minutes  to  24  hours.  The  charge  can  then  be  poured  and 
washed  through  a  coarse  screen  (to  retain  the  pebbles)  into  a  bucket 
and  thence  into  the  flotation  machine.  The  oxidation  of  sulphide 
surfaces  is  thus  avoided,  but  separate  grinding  of  each  charge, 
in  order  to  know  its  exact  weight,  is  rather  tedious  and  requires  a 
number  of  small  mills  if  many  tests  are  being  run,  on  account  of 
slow  speed  in  grinding.  A  mill  with  iron  balls  rather  than  pebbles 
is  of  greater  service.  It  is  possible  to  introduce  the  flotation-oil  before 
grinding,  to  be  sure  that  it  will  be  thoroughly  mixed.  For  thick 
viscous  oils  this  is  highly  beneficial,  as  a  ball-mill  gives  about  the 
best  conditions  for  agitation  and  mixing.  Usually  1  to  2  Ib.  charges 
are  used  and  a  small  laboratory  mill  of  the  Abbe  type  serves  well, 
although  a  good  mill  can  be  made  with  a  10-in.  length  of  8-in. 
iron  pipe  and  two  heavy  iron  caps  for  the  same. 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS — II  301 

Practice  in  our  laboratory  has  been  standardized  to  a  miniature 
gyratory  crushing  to  10-mesh,  splitting  into  weighed  samples  kept  in 
paper  bags  and  reduced  to  smaller  size  by  either  wet  or  dry  grinding 
as  occasion  demands. 

A  short-stemmed  tin  funnel  about  6  inches  in  diameter  with  a 
one-inch  opening  is  found  to  be  about  the  most  convenient  means 
of  pouring  a  charge  of  ore  into  a  laboratory  flotation-machine. 

The  measuring  and  testing  of  flotation-oils  in  the  labora- 
tory has  been  very  inexact  in  many  instances  witnessed  by 
us.  It  is  common  practice  to  count  the  number  of  drops  of 
oil  falling  from  a  small  piece  of  glass  tubing.  We  are 
using  a  Mohr  pipette  of  1  c.c.  total  capacity  for  measure- 
ment of  the  amount  of  oil  used  in  each  test.  Such  a  pipette 
is  shown  in  full  size  in  Fig.  73.  It  will  be  seen  that  this 
pipette  allows  measurements  of  the  oil  to  the  nearest  0.01 
c.c.,  which  is  as  close  as  will  ever  be  desired.  If  the  density 
of  the  oil  is  known,  the  volume  as  measured  by  this  method 
is  quickly  converted  into  the  weight  of  oil  used. 

The  testing  of  oil  samples  for  flotative  power  is  a  matter 
that  needs  standardizing.  It  is  desirable  to  classify  oils 
according  to  flotative  power,  but  just  how  to  do  this  is  not 
exactly  clear.  A  unit  of  '  flotativeness '  might  be  established 
and  each  oil  referred  to  that  unit  in  terms  of  percentage. 
But  it  has  to  be  remembered  that  the  best  oil  for  one  ore 
may  not  prove  to  be  the  best  oil  for  another,  although  two 
such  series  of  oils  might  roughly  parallel  each  other.  For 
any  given  ore,  it  would  be  permissible  to  make  such  a 
measurement  on  a  series  of  oils  and  group  them  according 
to  some  definite  standard.  A  standard  oil  might  be  chosen 
and  the  value  of  a  second  oil  expressed  in  percentages  of 
the  flotative  power  of  the  first  as  determined  by  using 
equal  quantities  of  the  two  oils  in  tests  on  an  ore  under 
identical  conditions.  This  test  could  not  be  fair  for  the 
reason  that  different  amounts  of  two  different  oils  are 
necessary  to  accomplish  the  same  results.  Further,  the 
conditions  of  acidity  or  alkalinity  might  favor  one  oil  and 
handicap  another.  If  we  measured  the  amount  of  oil 
necessary  to  give  a  fixed  percentage  of  extraction  the  first 
of  the  above  objections  would  be  satisfied,  but  conditions 
of  acidity  or  alkalinity  could  make  the  test  unfair  for 
some  oils.  Hence  the  dilemma  as  to  a  standardized  test  of  „„«« 

lVLU.rLrt  o 

a  flotation-oil.  PIPETTE. 


302  THE  FLOTATION  PROCESS 

No  single  test  could  definitely  place  an  oil  in  any  scheme  of 
classification  and  nothing  can  be  done  but  run  a  series  of  tests  using 
varying  amounts  of  the  oil  to  be  tested  and  with  varying  acidity  or 
alkalinity.  »  The  temperature  of  the  pulp  must  be  kept  constant 
although  it  has  a  minor  effect. 

Coutts  gives  about  the  only  directions  on  oil  testimg  that  are  to 
be  found  in  the  literature  of  the  subject6.  He  states  rightly  that 
the  first  thing  to  do  with  an  oil  is  to  measure  its  density,  for  future 
calculations,  as  it  will  be  measured  by  volume  in  the  laboratory 
and  must  later  be  reduced  to  weights.  He  recommends  the  use  of 
a  burette  for  measuring  the  oil,  but  we  favor  the  Mohr  pipette 
mentioned  above.  He  chooses  a  standard  ore  on  which  all  tests  are 
to  be  run  and  classifies  three  different  kinds  of  standard  tests: 
(1)  for  mixed  sulphides,  (2)  differential  separation,  and  (3)  flotation 
of  copper  and  iron  sulphides.  He  states  that  oils  high  in  phlanderene 
have  proved  best  for  differential  separation  of  zinc-lead  sulphide 
ores.  While  this  is  helpful,  he  does  not  state  just  how  the  oils  are 
to  be  classified  after  the  tests  have  been  made. 

Much  work  with  oils  is  needed  in  order  to  determine  if  there  are 
any  definite  constituents  in  oils  that  give  them  flotation  power. 
Research  is  also  needed  in  the  preparation  of  oils  from  the  wood, 
coal,  and  mineral  oils  in  such  a  manner  that  they  will  have  maximum 
efficiency  in  flotation.  Work  on  this  subject  has  been  initiated  in 
our  own  laboratory  and.  it  is  known  that  several  of  the  larger 
companies  have  employed  oil  chemists  to  look  into  such  problems. 
We  understand  that  most  excellent  work  is  being  done  on  methods 
of  modifying  and  reconstructing  oils  that  can  be  had  cheaply.  By 
this  we  mean  more  than  mere  mixing  of  a  good  flotation  oil  with  a 
cheaper  non-selective  oil.  Sulphonating  the  oils,  dissolving  them 
in  acids,  dissolving  modifying  substances  in  the  oils,  etc.,  are  some 
of  the  ideas  being  tested  with  varying  success.  It  is  on  account 
of  all  this  oil  testing  that  considerable  progress  has  been  made  in 
flotation  during  the  past  year,  so  that  now  most  of  the  larger 
companies  are  using  cheaper  oils  than  a  year  ago. 

When  starting  to  work  with  a  new  ore,  there  is  needed  a  rapid 
qualitative  method  of  choosing  an  oil  that  seems  well  adapted  to 
the  flotation  of  the  ore  in  question.  Such  a  scheme  is  in  use  in 
the  laboratory  of  the  General  Engineering  Company  at  Salt  Lake 
City.  Their  qualitative  tester  is  designed  to  test  oils  for  use  in  the 
Callow  pneumatic  flotation  cell  and  consists  of  a  glass  tube  of  about 


6J.  Coutts.    E.  &  M.  J".,  Vol.  XCIX,  page  1079  (1915). 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS — II  303 

two  inches  diameter  and  two  feet  long.  (Pig.  74.)  This  can  be 
set  on  end  and  closed  at  the  bottom  with  a  one-hole  rubber  stopper 
through  which  passes  a  glass  tube  into  a  small  canvas  bag.  The 
small  bubbles  of  air  coming  through  the  canvas  are  similar  to  those 
used  in  large-scale  machines  and  can  be  observed  through  the  glass 
walls  of  the  tube.  With  some  pulp  in  the  tube,  oils,  acids,  salts,  etc., 
may  be  added  in  very  short  tests  until  the  proper  appearance  is 
obtained.  An  overflow  lip  is  provided  in  case  it  is  desired  to  examine 
the  mineral  in  the  froth.  A  slight  adjustment  of  the  air  will 
provide  an  ample  overflow  of  froth. 

DISPOSAL  OF  THE  FROTH.     The  handling  of  the  flotation  froth 
in  the  laboratory  finds  difficulties  which  are  reflected  in  practice. 


i^V^J 


Pulp. 


Air. 


PIG.   74.      QUALITATIVE  OIL  TESTEB. 

It  is  often  very  slow  to  settle  and  filters  with  difficulty.  A  vacuum- 
filter,  connected  with  a  laboratory  aspirating  pump,  is  a  very 
convenient  method  of  getting  the  concentrate  out  of  the  froth.  A 
large  porcelain  Buechner  funnel  fitted  into  a  filtering  flask,  as  shown 
in  Fig.  60,  is  used  at  present  in  our  laboratory.  A  copper  vacuum- 
filter  of  much  the  same  type,  provided  with  a  porous  false  bottom 
of  acid-proof  wire  cloth,  resting  on  a  punched  plate,  is  shown  in 
Fig.  71  of  the  Callow  test  set.  Filter-papers  can  be  laid  over  the 
bottom  of  either  of  these  funnels  to  collect  the  concentrates,  and 
the  vacuum  beneath  sucks  out  the  water  and  oil  of  the  froth.  Such 
a  filter  can  be  placed  under  the  froth-discharge  of  a  flotation  machine 
so  that  a  fairly  dry  cake  of  concentrate  is  ready  for  further  drying 
at  the  end  of  the  flotation  test.  By  loosening  the  outer  rim  of  the 
filter-paper  and  then  turning  the  funnel  upside  down  over  a  pan,  the 
filter-paper  with  the  concentrate  can  be  dropped  into  the  drying-pan 
by  gently  blowing  into  the  stem  of  the  funnel.  This  is  set  aside  in 
a  warm  place  to  dry  and  later  weighed  against  a  filter-paper  tare. 
If  it  is  desired,  the  froth  can  be  collected  in  a  glass  beaker  or 


304  THE   FLOTATION   PROCESS 

other  vessel  and  allowed  to  stand  over-night.  A  layer  of  clear 
water  can  then  be  siphoned  off  and  the  thick  pulp  remaining  filtered 
or  dried  direct.  In  some  laboratories  the  froth  is  dumped  onto  a 
shallow  pan  on  a  hot  plate  and  the  water  evaporated.  Occasionally 
such  a  sample  of  froth  will  be  left  too  long,  and  will  be  ignited 
and  roasted.  We  once  used  a  numbered  set  of  shallow  pans  for  such 
evaporations  but  prefer  filtering  before  drying  the  precipitate.  A 
numbered  tag  is  now  put  in  each  pan  along  with  the  cake. 

The  products  coming  from  the  flotation  machine  should  be 
watched  closely  and  occasionally  panned  or  examined  with  the 
microscope  to  see  what  kind  of  work  is  being  done.  This  is  fairly 
easy  to  determine  as  the  sulphides  are  most  of  them  distinguished 
easily  from  the  gangue  under  the  microscope,  and  likewise  gangue 
particles  in  the  froth-concentrate  can  often  be  distinguished.  A 
microscope  is  a  most  useful  adjunct  in  a  flotation  laboratory  or  mill. 

GENERAL  CONSIDERATIONS.  We  have  mentioned  at  various  places 
the  relation  of  the  laboratory  tests  to  the  large-scale  operations  and 
now  repeat  that  in  almost  every  instance  the  laboratory  results  are 
somewhat  pessimistic  as  compared  to  large-scale  work.  The  reasons 
are  made  apparent  by  the  smallness  of  the  machine  and  the  shallower 
layer  of  froth  often  formed  under  these  conditions.  Moreover,  labora- 
tory operations  seem  to  call  for  greater  amounts  of  oil,  acid,  etc., 
than  do  the  large-scale  operations. 

Only  one  of  the  above  machines  is  adapted  to  'roughing'  and 
1  cleaning '  operations  in  a  single  test.  Present-day  practice  tends 
toward  re-treatment  of  at  least  part  of  the  froth  in  order  to  make 
cleaner  and  higher-grade  concentrates.  Consequently,  it  may  be 
desirable  to  collect  enough  froth  from  a  series  of  tests  to  be  re-treated 
in  a  *  cleaning '  test.  Of  course,  this  is  provided  for  in  the  Callow 
test  set,  where  only  'cleaned'  concentrate  is  discharged  from  the 
machine.  It  is  further  found  desirable  to  weigh  and  analyze  some 
of  the  successive  fractions  of  the  froth  being  discharged  from  a 
flotation  machine,  as  the  tailing  becomes  leaner,  and  determine  at 
what  point  it  may  be  desirable  to  re-treat  such  froth. 

Many  reports  of  flotation  test-work  with  mechanical-agitation 
machines  give  the  speed  of  the  rotation  of  the  agitating-blades.  We 
have  found  that  it  was  possible  to  get  much  the  same  work  done 
with  quite  a  variation  of  speeds,  the  only  effect  being  to  lengthen 
or  shorten  the  time  of  treatment.  We  feel  that  the  importance  of 
this  matter  has  been  much  exaggerated.  Some  means  of  speed- 
control  is  necessary  and  the  speed  can  be  adjusted  in  each  case  until 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS II    . 


305 


FIG.   75.      THE  CASE  MACHINE. 


the  froth  presents  the  proper  appearance  as  to  depth,  size  of  bubbles, 
color,  etc.  Speeding  toward  the  end  of  a  test  in  order  to  give  a 
deeper  froth  with  a  faint  line  of  concentrate  on  the  very  top  is  often 


306  THE  FLOTATION  PROCESS 

advisable.  We  recommend  adjusting  the  speed  in  each  test  to  suit 
the  other  conditions,  rather  than  running  a  series  of  tests  with 
different  speeds.  Only  in  the  slide  machine,  where  operation  of 
the  impeller  must  be  suspended  in  order  to  allow  froth  to  collect, 
is  the  speed  of  much  importance.  Here  we  recommend  agitation  for 
a  definite  length  of  time,  and  then  a  period  of  settling.  The  effect 
of  variation  of  speed  during  a  definite  length  of  time  may  be  a 
considerable  variation  in  the  amount  of  froth  collected  during  the 
quiet  period.  Hence  we  are  prejudiced  against  the  use  of  the  slide 
machine  except  for  oil-testing. 

When  a  good  set  of  conditions  has  been  found  for  the  flotation 
treatment  of  an  ore,  it  is  best  to  recover  the  water  from  each  test  to 
see  what  effect  a  closed  circuit  of  the  mill-water  will  have.  Some 
oil  and  chemicals  are  thus  recovered,  cutting  down  the  amounts 
necessary  for  operation.  In  fact,  a  carboy  or  two  of  the  water  to 
be  used  in  the  large  mill  should  be  used  to  make  certain  that  no 
deleterious  contamination  will  ensue  from  this  source.  Under  these 
conditions  filtration  of  the  concentrate  and  tailing  for  recovery  of 
the  water  is  necessary.  Such  conditions  are  provided  for  in  the 
Callow  apparatus,  above  described,  and  can  be  applied  easily  to 
any  of  the  other  machines. 

Oil  samples  for  test  purposes  can  be  obtained  from  the  various 
wood-distilling  companies  now  advertising  in  the  technical  press, 
from  gas  companies  and  from  petroleum-refining  companies. 

In  attacking  refractory  ores,  there  are  a  number  of  ingenious 
things  that  can  be  done  to  the  pulp  both  in  and  out  of  the  machine. 
The  trouble  may  be  due  to  deleterious  substances,  which  sometimes 
can  be  washed  out,  rendered  harmless  by  boiling,  or  by  acidifying, 
or  by  making  alkaline  with  lime  before  entering  the  machine. 
Occasionally,  the  ore  will  not  work  well  under  ordinary  conditions 
but  will  yield  beautifully  after  finer  grinding.  Sometimes  extra 
reagents  are  necessary,  such  as  powdered  charcoal,  modified  oils, 
argol,  soap,  calcium  sulphate,  alum,  etc.  A  rational  method  of 
devising  the  proper  tests  in  such  cases  must  be  based  on  some  theory 
of  flotation.  Colloid  chemistry  is  a  branch  of  knowledge  that  we 
believe  to  be  very  necessary  for  such  work,  as  it  has  facilitated  a  more 
intelligent  control  of  our  tests  and  has  given  wonderful  results  in 
a  number  of  instances. 

Finally,  it  is  well  to  be  prodigal  in  the  amount  of  analytical  work 
connected  with  flotation  testing  in  order  to  discover  interesting 
differences  in  gangue-constituents  carried  into  the  concentrate,  as 


TESTING  ORES  FOR  THE  FLOTATION  PROCESS — II         307 

well  as  to  find  the  best  conditions  for  leaving  out  some  gangue 
constituent  that  is  less  desirable  than  the  rest.  If  an  experimenter 
does  his  own  analytical  work  he  can  be  expected  to  spend  three-fourths 
of  his  time  analyzing  what  has  been  done  during  the  other  fourth. 

Summarizing  the  most  important  points  to  be  tested  on  a  given 
ore  with  any  given  flotation  machine,  we  have: 

Method  of  grinding. 

Fineness  of  grinding. 

Kind  of  frothing  agent  used. 

Amount  of  frothing  agent. 

Acidity  or  alkalinity. 

Temperature. 

Necessity  of  preliminary  agitation. 

Effect  of  addition-agents  in  flocculating  gangue-slime. 

It  can  be  seen  that  there  may  be  a  certain  best  combination  of 
the  above  variables  that  will  be  entirely  missed  if  a  great  many 
tests  are  not  carried  out;  hence  the  desirability  of  doing  the  testing 
in  a  small  laboratory-machine  where  many  trials  can  be  made  in  a 
short  time. 

After  the  best  conditions  have  seemingly  been  established,  they 
should  be  further  tried  in  a  larger-sized  machine  before  they  are 
incorporated  into  the  general  practice  of  a  mill.  The  test-work 
on  this  scale  need  hardly  be  described,  as,  for  the  most  part,  it 
is  a  question  of  translation  of  laboratory  results  into  large-scale 
operation. 

[We  have  added  an  illustration  of  the  Case  machine,  evidently 
a  modified  Hoover  apparatus,  made  by  the  Denver  Fire  Clay  Co. — 
EDITOR.] 


308  THE  FLOTATION  PROCESS 

MOLECULAR  FORCES  IN  FLOTATION 

Surface  Compression 

By  DUDLEY  H.  NORRIS 
(From  the  Mining  and  Scientific  Press  of  February  12,  1916) 

At  the  meeting  of  the  local  membership  of  the  American  Institute 
of  Mining  Engineers  on  December  14  last  the  question  was  asked  by 
one  of  the  speakers:  "Why  does  the  greased  needle  float  on  the  surface 
of  a  tumbler  of  water  and  the  wetted  needle  sink?"  Did  one  or 
another  of  the  experts  present  rise  and  say  that  it  was  due  to  'surface 
tension '  and  then  in  a  few  well  chosen  words  explain  jnst  exactly  what 
'surface  tension'  is?  Nothing  of  the  sort  happened.  The  question 
was  not  only  not  answered,  but  it  was  unanimously  avoided.  It  is  a 
fair  question,  however,  and  deserves  an  answer. 

The  fact  is  that  'surface  tension '  is  a  misnomer.  Tension  is  a 
stretching,  whereas  the  phenomena  in  question  are  those  of  com- 
pression. In  'surface  tension/  a  bubble  of  air  or  a  drop  of  water 
is  pictured  to  the  imagination  as  being  actually  of  the  form  that  it 
would  have  if  it  were  contained  in  a  film  like  that  of  a  soap-bubble  or  a 
toy-balloon.  That  grasped,  the  substance  of  the  bubble  or  of  the  drop  is 
ignored  and  we  are  asked  to  occupy  our  minds  only  with  the  imaginary 
film.  The  reasoning  appears  to  be:  "There  might  be  such  a  film, 
there  must  be,  there  is.  Otherwise,  we  are  not  able  to  explain  it  at 
all."  In  what  follows,  I  shall  attempt  to  explain  the  phenomena  dis- 
cussed in  terms  of  molecular  attraction  and  of  heat. 

If  you  will  fill  a  tumbler  with  water  or  other  liquid  and  then  con- 
tinue carefully  to  pour  in  more;  instead  of  running  over  the  side, 
there  will  be  a  heaping  up  of  the  liquid  in  the  tumbler  and  a  rounding 
of  the  surface,  the  centre  of  the  liquid  being  as  much  as  a  sixteenth 
or  even  an  eighth  of  an  inch  higher  than  the  rim  of  the  tumbler.  That 
is  the  phenomenon  of  your  'surface  tension'  pure  and  undefiled.  The 
same  phenomenon  is  seen  when  mercury  is  contained  in  a  glass  ves- 
sel, even  when  the  vessel  is  only  partly  filled.  Mercury  does  not  wet 
glass,  and  where  the  liquid  metal  meets  the  side  of  the  glass  vessel  the 
mercury  is  convex.  Where,  however,  the  tumbler  is  only  partly  filled 
with  water  the  surface  of  the  water  is  concave  where  it  meets  the 
inside  of  the  tumbler,  and  the  glass  is  wetted  by  the  water. 

In  the  Miami  flotation  case  it  was  stated  that  surface  ten- 
sion is  a  force  existing  in  the  surface  of  a  liquid  that  tends 
to  draw  the  liquid  into  the  form  of  a  sphere,  this  being 


MOLECULAR  FORCES  IN  FLOTATION — SURFACE  COMPRESSION          309 

the  most  compact  form  that  a  given  volume  can  assume  and 
the  form  in  which  it  presents  the  least  surface.  This  is  a 
lovely  specimen  of  the  logical  fallacy  known  as  post  hoc  ergo  prop- 
ter  hoc.  In  surface  tension,  it  was  said  in  the  Miami  case,  because 
the  most  compact  form  that  a  given  volume  can  assume  and  the  form 
in  which  it  presents  the  least  surface  is  a  sphere,  therefore  the  volume 
assumes  that  form  and  does  so  at  the  behest  of  surface  tension ;  but  as 
to  the  why  and  how,  nothing  was  said,  nor  can  they  be  imagined.  It 
reads  as  if  there  had  been  a  mass-meeting  of  the  molecules  looking 
to  'preparedness. '  The  molecule  acting  as  chairman  states  the  business 
before  the  assembled  molecules :  * '  Owing  to  the  war  in  Europe  and  a 
hard  winter  coming  on,  the  molecules  must  decide  on  some  form  that 
will  be  the  most  compact  and  which  will  present  the  least  possible 
surface  to  an  unsympathetic  world.  The  sphere  comes  highly  recom- 
mended. It  is  moved  and  seconded  therefore  that  the  molecules  form 
a  sphere.  So  ordered." 

The  calculus  proposition  that  two  homogeneous  spheres  attract 
each  other  as  if  their  masses  were  collected  at  their  centres  of  gravity 
is  as  true  as  anything  human  can  be.  It  is  also  true  that  in  a  single 
homogeneous  sphere,  if  acted  on  by  no  outside  force,  the  cohesive 
attraction  of  its  molecules  for  each  other  will  act  radially  toward  the 
centre  and  form  a  sphere ;  and  it  is  this  radial  attraction  and  not  an 
imaginary  film  or  a  non-existent  tension,  that  causes  the  phenomenon, 
and  it  is  probably  some  similar  molecular  attraction  that  causes 
mineral  flotation. 

In  James  Clerk  Maxwell's  article  on  capillary  action,  in  the  En- 
cyclopcedia  Britannica  (llth  edition),  vol.  5,  p.  258,  he  says:  " Plateau, 
who  made  an  elaborate  study  of  the  phenomena  of  surface  tension, 
adopted  the  following  method  of  getting  rid  of  the  effects  of  gravity. 
He  formed  a  mixture  of  alcohol  and  water,  of  the  same '  density  as 
olive  oil,  and  then  introduced  a  quantity  of  oil  into  the  mixture.  It 
assumes  the  form  of  a  sphere  under  the  action  of  surface  tension 
alone."  That  it  assumes  the  form  of  a  sphere  is  granted.  That  sur- 
face tension  does  it  is  denied. 

The  toy-balloon  has  a  place  in  a  rational  explanation  of  the  phe- 
nomena under  discussion ;  but  the  alleged  film  around  a  drop  of  water 
or  around  a  bubble  of  air,  or  as  the  top  layer  of  a  body  of  water,  like 
the  film  of  a  toy-balloon,  has  no  existence  in  nature.  The  vendor  of 
toy-balloons  has  each  one  of  his  gayly  colored  stock  fastened  by  a 
string,  which  serves  the  double  purpose  of  keeping  the  gas  in  the 
balloons  and  of  keeping  the  balloons  themselves  down  to  earth.  The 


310 


THE   FLOTATION   PROCESS 


free  ends  of  the  strings  are  brought  to  a  common  knot.  There  is  a 
pull  on  each  string  along  the  hypothenuse  of  a  right-angle  triangle; 
this  can  be  resolved  into  a  vertical  component,  tending  to  make  the 
balloon  float  off,  and  a  horizontal  component,  tending  to  crowd  the 
balloons  together. 

The  same  thing  happens  in  surface  compression.  The  water  in  the 
tumbler  is  subject  to  the  cohesive  attraction  of  its  molecules,  to  the 
attraction  of  gravitation,  and  to  heat.  The  water,  if  free  from  the 
attraction  of  gravitation,  would  tend  to  form  a  sphere,  but  gravitation 
causes  it  to  conform  to  the  shape  of  the  containing  vessel.  Heat,  by 
tending  to  drive  the  molecules  apart,  acts  counter  to  the  attraction 
of  cohesion  and  their  equilibrium  fixes  the  specific  gravity  of  the 
water,  its  bulk,  and  its  state  of  aggregation — making  it  solid,  liquid, 
or  gaseous  as  the  case  may  be.  If  gravitation  be  neutralized  or  be  not 
opposed,  the  water  takes  a  spherical  form  under  the  influence  of  co- 
hesion, as  is  shown  in  raindrops,  in  Plateau's  experiment,  and  in  drops 
of  water  on  a  hot  stove,  in  conformity  with  the  rule  of  homogeneous 
spheres. 

Let  us  suppose  each  molecule  of  water  in  the  tumbler  to  be  free 
from  the  attraction  of  gravitation  and  in  the  form  of  a  sphere,  -then 
the  vertical  section  of  the  surface  layer  would  look  like  this : 


Surface 
Compre 


Centre  o/ Gravity 

FIG.    76.      FORCES   AFFECTING  SURFACE  OF  WATER. 

There  you  have  the  stock  of  toy-balloons  with  the  strings  connect- 
ing each  with  a  common  centre  point.  C  is  the  centre  of  gravity  of 
the  water  in  the  glass.  The  lines  diverging  from  C  show  the  direc- 
tions of  the  forces  of  cohesion.  The  short  vertical  lines  downward 
from  each  molecule  indicate  the  lines  of  the  force  of  gravity  and  the 
arrowheads  on  the  cohesion  lines  mark  the  opposing  forces  of  heat 


MOLECULAR  FORCES  IN  FLOTATION SURFACE  COMPRESSION 


311 


and  cohesion.  In  the  triangle,  C  a  d,  for  example,  the  hypothenuse 
C  d  represents  the  total  force  of  cohesion ;  C  a  is  its  vertical  component, 
and  a  d  its  horizontal  component.  The  resultant  of  all  these  hori- 
zontal components  ad,  ac,  ab,  etc.,  is  a  force  effecting  a  compression  of 
the  surface  of  the  water.  A  good  idea  of  the  structure  of  surface 
compression  is  shown  by  the  ripe  seed-tuft  of  the  common  dandelion. 

Oh,  but  water  is  not  compressible.  True  enough,  to  any  sensible 
degree  by  an  exterior  force ;  but  the  interior  forces  at  work  in  water 
do  many  wonderful  things.  For  instance,  they  cause  water  to  ex- 
pand on  cooling  and  to  contract  on  heating,  between  0°C.  and  4°C., 
and  all  the  water  phenomena  of  oceans,  rivers,  and  rain-fall,  of 
hydraulic  and  of  steam  powers,  and  of  the  irresistible  force  of  freez- 
ing, are  caused  by  the  molecular  activities  existing  in  a  drop  of 
water. 

One  reason  for  lack  of  a  clearer  understanding  of  these  phe- 
nomena is  the  failure  to  perceive  the  fact  that  the  tendency  to  form 
a  sphere  of  water  in  the  tumbler  is  incessant,  whether  the  attraction 
of  gravitation  acts  on  the  mass  of  the  water  freely,  as  in  falling;  is 
warded  off,  as  in  Plateau's  experiment;  or  is  super-imposed  upon  the 
attraction  of  cohesion,  compelling  the  water  to  conform  to  the  in- 
terior shape  of  the  tumbler  and  rendering  the  ever-present  cohesion 
inconspicuous. 

The  action  of  water  from  the  higher  degrees  of  temperature, 
through  4°  C.  to  ice,  is  shown  by  the  accompanying  drawings.  A  mole- 

FIG.  77. 


VOLUME    ABOVE    4°    C. 


VOLUME   AT    4°    C. 


VOLUME    AS    ICE. 


cule  of  water,  composed  of  three  atoms,  is  plausibly  represented  by  a 
triangle.  Two  such  molecules  are  separated  a  certain  distance  by  a 
corresponding  amount  of  heat,  and  this  distance  fixes  the  volume  of 
the  mass  of  water,  which  increases  and  diminishes  as  the  degree  of 
heat  is  raised  or  lowered.  At  4°  the  volume  of  water  is  at  a  minimum 
and  it  is  a  fair  inference  that  the  molecules  of  water  are  at  that  point 


312  THE  FLOTATION  PROCESS 

nearer  to  each  other  than  at  any  point.  Below  4°C.  the  molecular 
forces  react  in  such  a  manner  as  to  cause  a  change  in  the  relations  of 
the  molecules  themselves,  causing  them  to  turn  and — in  the  state  of 
ice — to  assume  the  positions  shown  in  the  third  figure,  with  a  lower 
specific  gravity  than  the  water  had  before  freezing.  No  other  forces 
are  necessary  to  the  causation  of  the  phenomena  indicated  than  those 
of  cohesion  and  heat. 

Here,  then,  is  the  answer  to  the  question  asked  at  the  meeting: 
By  reason  of  the  horizontal  components  of  the  attractions  of  co- 
hesion which  draw  each  molecule  of  water  toward  the  centre  of 
gravity  of  its  mass,  the  surface  of  the  water  is  compressed,  made 
more  dense,  and  offers  a  resistance  to  the  needle  greater  than  the 
weight  of  the  needle.  That  weight  is  not  sufficient  to  break  apart 
the  surface  molecules,  but  only  makes  a  slight  indentation  on  the 
surface.  When  the  needle  is  wetted,  capillary  attraction  raises  the 
compressed  surface  over  and  above  the  needle  which,  no  longer 
resting  upon  the  denser  surface,  but  in  water  not  under  surface 
compression,  obeys  the  attraction  of  gravitation  and  sinks. 

Attention  was  called  above  to  the  two  cases  of  simple  compres- 
sion where  the  entire  surface  of  both  liquids,  the  water  in  the  brim- 
full  tumbler  and  the  mercury  in  the  partly  filled  glass  vessel,  are 
convex,  whereas  in  a  tumbler  partly  filled  with  water,  the  edge  of 
the  water,  where  it  meets  the  glass  composing  the  tumbler,  is  con- 
cave and  the  water  wets  the  glass.  Thus  there  is  added  a  new  force 
which  modifies  the  surface  compression  of  the  water  and  draws  the 
water  at  the  edge  upward  on  the  glass,  forming  a  concavity  tangent 
to  both  the  surface  of  the  water  and  the  inside  of  the  tumbler.  It 
makes  no  difference  here  and  now  what  this  force  is  called,  whether 
cohesion  or  adhesion;  whether  it  is  the  same  molecular  attraction 
that  exists  between  the  molecules  of  the  water  or  whether  it  is  the 
cohesion  of  the  glass  acting  at  sensible  distances,  or  neither,  or  both. 
The  water  is  drawn  up,  not  pushed  up,  and  any  drawing  up  is  attrac- 
tion, and  acting  on  molecules  it  is  molecular  attraction. 

In  a  tumbler  2£  inches  in  diameter  the  horizontal  concavity 
against  the  glass  seemed  to  be  about  TV  °f  an  incn  wide,  perhaps  a 
little  more,  leaving  about  2|  in.  of  convexity  to  -J  in.  total  concavity, 
out  of  the  diameter  of  2J  in.  The  vertical  concavity  seemed  also 
about  TV  of  an  inch  along  the  inside  of  the  glas-s.  With  glass  tubes 
of  smaller  diameter  the  horizontal  concavity  seemed  to  remain 
about  the  same,  but  the  vertical  concavity  increased  as  the  diam- 
eter diminished.  The  convexity  at  the  centre  of  the  surface  de- 


MOLECULAR  FORCES  IN  FLOTATION — SURFACE  COMPRESSION          313 

creased  with  the  diameter  of  the  circle  and  in  a  tube  of  J  in.  diam- 
eter the  surface  of  the  water  was  an  inverted  hollow  sphere  with  no 
convexity  at  all  and  its  height  above  the  level  of  the  water  in  the 
tumbler  was  J  of  an  inch.  With  a  tube  of  ^  in.  diameter  the  water 
came  up  ^  inch. 

The  surface  compression  at  the  edge  of  the  water  in  the  tumbler 
is  less  than  nearer  the  centre,  being  practically  zero,  and  offering 
no  resistance  to  the  upward  attraction  upon  the  water.  If  a  glass 
tube  be  partly  immersed  in  the  water  in  the  tumbler,  the  water  in 
the  tube,  even  if  open  at  the  lower  end,  forms  a  separate  cohesive 
mass,  independent  of  the  rest  of  the  liquid  with  all  the  'phenomena 
of  capillarity. 

It  has  been  said  above  that  the  cohesion  of  the  water  varies  in- 
versely as  the  temperature,  being  greater  at  the  lower  than  at  the 
higher  temperatures,  and  at  the  boiling  point  there  is  no  cohesion. 
With  the  same  changes  in  temperature  the  attraction  between  the 
water  and  the  glass  sides  of  the  tumbler  varies  exactly  as  the  co- 
hesion varies,  and  there  is  every  reason  to  believe  that  the  forces 
elevating  the  liquid  are  those  of  cohesion  of  the  water  and  the  glass 
acting  at  sensible  distances.  These  phenomena  between  the  water 
and  the  mercury  on  one  hand  and  glass  on  the  other  are,  of  course, 
those  of  capillarity.  They  seem  to  fit  in  with  the  above  theory  of 
surface  compression. 

Then  what  is  there  left  of  true  surface  tension  ?  Well,  there  is  the 
soap-bubble.  I  made  some  experiments  in  this  direction  a  few  days 
ago  with  50  or  60  soap-bubbles  from  4  to  6J  inches  in  diameter.  These 
were  burst  over  a  dark  hardwood  table  about  30  inches  square,  so  that 
the  resulting  wet  spots  on  the  surface  of  the  table  could  be  examined. 
Care  was  taken  in  every  case  in  blowing  the  bubbles  to  remove  the 
usual  drop  of  water  at  the  south  pole  of  the  bubble,  so  that  all  the 
wet  spots  came  from  the  wreck  of  the  distended  film.  After  each 
bubble  burst  the  table  was  wiped  dry  for  the  next  one.  When  infla- 
tion ceased,  one  bubble  5  inches  in  diameter  shrank  an  inch  before  it 
burst ;  another  shrank  from  6J  to  5  inches.  In  both  cases  the  air  was 
expelled  by  a  real  surface  tension  of  the  bubble's  film.  Most  of  the 
bubbles  were  blown  until  they  burst,  at  from  1  inch  to  2  feet  above 
the  table.  The  ones  at  1  inch  spread  wet  spots  in  circles  from  7  to 
13  inches  in  diameter.  Of  the  bubbles  that  burst  at  greater  distances 
from  the  table,  at  6  inches  above  the  table  the  wet  spots  extended  to- 
the  edge  of  a  circle  15  inches  in  diameter;  at  12  inches  above,  20 
inches;  at  20  inches,  24  inches;  and  at  24  inches,  30  inches.  Count- 


314  THE  FLOTATION  PROCESS 

ing  a  quarter  circle,  there  were  from  175  to  260  wet  spots,  or  700  to 
1000  for  each  bubble. 

It  was  evident  that  the  force  throwing  these  drops  of  water  such 
great  distances  was  not  the  air  pressure  inside  the  bubble.  When  the 
bubble  burst  the  attraction  of  cohesion  of  the  water  composing  the 
film  acted  to  re-unite  the  distended  watery  molecules  and,  as  the 
shortest  distance  between  two  points  on  the  circumference  of  a  sphere 
is  measured  on  the  great  circle  that  joins  them,  the  re-uniting  molecules 
took  that  route,  traveling  over  the  spherical  surface  of  the  bubble, 
and  when  a  number  of  them  met  and  formed  a  drop,  all  the  molecules 
were  attracted  with  a  certain  force.  The  tangential  components  of 
these  cohesive  forces,  acting  in  the  substances  of  the  spherical  film 
and  at  right  angles  to  the  bubbles'  radii/ neutralized  each  other,  while 
the  centrifugal  components  united  to  shoot  the  drops  away  from  the 
centre  of  the  late  bubble,  in  the  direction  of  the  prolongation  of  the 
bubbles'  radii,  and  they  fell  in  a  wide  circle,  as  already  stated. 

This  is  a  true  statement  of  the  phenomena  of  the  effect  of  surface 
tension  on  a  soap-bubble.  By  what  stretch,  by  what  torture,  of  the 
imagination  can  these  phenomena  be  brought  into  identity  or  even  the 
least  resemblance  with  those  of  the  placid  floating  of  the  greased  needle 
upon  the  compressed  surface  of  the  water  in  the  tumbler  ? 

Mr.  Charles  T.  Durell  in  an  article  in  the  Mining  and  Scientific 
Press  of  September  18,  1915,  entitled  'Why  Is  Flotation?',  discusses 
the  rising  of  a  bubble  through  a  liquid  and  says:  "Surface  tension 
causes  the  molecules  of  the  liquid  to  form  a  film  around  the  bubble 
and  remain  with  it  to  the  exclusion  of  like  molecules  during  the  time 
the  bubble  remains  in  the  liquid.  To  all  intents  and  purposes,  this 
film  is  seen  to  be  the  same  as  if  it  were  a  membrane  of  some  solid.  The 
air  in  these  bubbles  can  no  more. come  in  contact  with  the  liquid 
through  which  it  is  passing  than  it  could  were  it  inside  a  toy  balloon, 
for  instance.  The  bubble  may  be  said  to  be  enclosed  in  a  '  liquid  skin. ' 
As  a  proof  of  his  argument  he  cites  in  a  footnote  the  following :  "A 
striking  experiment  to  show  these  liquid  films  is  as  follows:  To  a 
breaker  partly  filled  with  a  colorless  oil,  add  a  small  quantity  of  per- 
manganate solution.  Blow  air  through  a  finely  drawn-out  glass  tube 
into  the  permanganate  solution  now  on  the  bottom  of  the  beaker.  Air 
bubbles  enclosed  in  the  colored  liquid  film  rise  through  the  oil  and 
break  at  the  surface,  because  of  the  expansive  force  of  the  gas.  The 
colored  water  drops  back  through  the  oil  exactly  in  the  same  manner 
that  a  balloon,  bursting,  drops  to  the  earth." 

With  these  instructions  the  following  experiments  were  made :     A 


MOLECULAR  FORCES  IN  FLOTATION — SURFACE  COMPRESSION          315 

layer  of  water,  half  an  inch  thick,  colored  dark  blue  with  a  dye  not 
soluble  in  kerosene,  was  put  into  a  tumbler  and  three  inches  of  white 
kerosene  poured  upon  it.  With  a  medicine  dropper  having  a  rubber 
.  bulb  and  a  -j^-in.  hole  in  the  end  of  the  glass  tube,  bubbles  of  air  were 
blown  into  the  blue  water,  the  end  of  the  glass  rod  resting  on  the 
bottom  of  the  tumbler.  At  first  the  pressure  on  the  bulb  was  made 
very  gently,  the  idea  being  to  have  the  bubbles  as  small  as  possible. 
As  many  as  200  of  these  tiny  bubbles  were  blown  and  they  rose  to  the 
surface  and  formed  a  group.  Some  burst,  some  were  incorporated 
with  others,  and  finally,  of  course,  they  all  burst.  Every  one  of  these 
200  bubbles  burst  within  a  circle  of  half  an  inch,  and  that  circle  from 
the  time  of  the  first  bubble  until  the  last  one,  was  not  free  from 
bubbles,  one  touching  another  and  all  forming  a  single  compact 
group ;  but  at  no  time,  in  the  strong  sunlight,  was  there  the  slightest 
trace  of  blue  in  the  circle  nor  anywhere  in  the  kerosene.  The  upward 
bound  bubbles  were  perfectly  white  and  there  were  no  return  pas- 
sengers. The  bubbles  had  no  films  but  were  simply  holes  in  the  water. 
When  they  came  to  the  joint  surface  of  blue  water  and  kerosene^ 
they  slipped  into  the  kerosene,  made  holes  in  that,  and  burst  at  the 
surface  with  no  trace  of  a  film. 

Then,  with  greater  pressure  on  the  bulb,  larger  bubbles  were  blown, 
and  with  them,  small  quantities  of  the  blue  water  were  forced  up 
into  the  kerosene.  When  these  came  separately  the  air  rose  to  the 
surface  and  the  water  dropped  back,  but  where  they  came  together 
the  air  buoyed  the  water  up  to  the  surface  where  the  air  escaped  and 
the  blue  water  sank  through  the  kerosene  and  disappeared.  With 
greater  pressure  the  bubbles  became  still  larger,  as  did  also  the  size 
of  the  drops  of  water  forced  out  with  the  air.  Where  trapped  together 
the  larger  masses  of  air  and  blue  water  joined  and  rose  to  the  surface, 
as  a  single  entity,  sometimes  very  rapidly  and  sometimes  very  slowly. 
But  in  no  case,  whatever  the  size  of  the  constituent  parts,  was  the 
air-bubble  blue.  There  were  never  any  water-films.  The  rising  com- 
bined air  and  blue-water  drops  in  the  cases  of  the  larger  bubbles  were 
in  shape  as  if  the  bubble  were  sitting  on  a  tiny  blue  feather  bed.  In 
every  case  the  blue  water  was  below  and  the  white  bubble  above  and 
the  bubble  was  pulling  the  drop  to  the  surface.  Sometimes  the  drop 
was  too  heavy  for  the  bubble  to  float  and  both  sank  to  the  water  layer 
and  remained  stationary  until  the  drop  merged  in  the  blue  water  and 
the  bubble  was  released. 

When  the  smaller  bubbles  rose  to  the  surface  of  the  kerosene  they  did 
not  break  as  quickly  as  in  water  but  seemed  to  strike  against  the 


316  THE  FLOTATION  PROCESS 

under  side  of  the  surface  stratum  and  rebound  downward  and  moving 
over  to  the  edge  of  the  tumbler.  On  nearing  the  glass  they  seemed 
to  rise  as  if  attracted  upwardly,  like  the  part  of  the  surface  stratum 
around  the  edge  under  capillary  attraction. 

Some  other  interesting  phenomena  of  capillarity  were  noticed.  In 
the  blue-drop-kerosene  experiment  the  sides  of  the  glass  were  wetted 
by  the  kerosene,  even  below  the  joint  surface  of  the  liquid;  but  not- 
withstanding this  fact  there  was  observed  the  concavity  of  the  blue 
water  under  the  oil,  seemingly  warranting  the  belief  that  the  attrac- 
tions between  the  water  and  the  glass  took  place  through  the  inter- 
mediate film  of  oil. 

With  a  body  of  mercury,  a  glass  tube  pushed  below  the  surface 
showed  a  rounded  surface  of  mercury  within  the  tube,  with  no  capil- 
larity, the  rounded  surface  being  due  solely  to  surface  compression. 
With  the  tube  floating  in  the  mercury  the  level  of  the  outside  mercury 
was  exactly  the  same  as  the  top  of  the  rounded  contents  of  the  tube ; 
but  when  the  tube  was  pressed  down  into  the  mercury  the  level  of  the 
mercury  in  the  tube  was  lowered.  It  seems  likely  that  the  indentation 
of  the  floating  needle  and  the  lowering  of  the  level  of  mercury  in  the 
glass  tube  are  both  due  to  the  resistance  of  the  surface  compression 
to  the  entrance  of  foreign  bodies. 

In  the  experiment  of  the  blue  water,  the  bubbles  and  the  kerosene, 
we  come  most  unexpectedly  upon  flotation,  or  its  counterfeit.  If  it  is 
flotation,  like  the  mineral  flotation,  how  is  it  to  be  accounted  for?  If 
it  is  different,  what  is  the  difference?  Will  an  explanation  of  the 
blue-drop  kerosene  flotation  be  that  of  mineral  flotation,  or  will  it 
help  in  that  direction  ?  There  is  surely  an  attraction  between  the  air- 
bubble  and  the  blue  drop,  or  why  should  they  stick  together?  The 
blue  drop  is  heavier  than  the  kerosene  and  the  bubble  of  air  lighter. 
One  pulls  up  and  the  other  pulls  down.  Why  do  they  not  separate 
unless  there  is  a  positive  molecular  attraction  between  them?  Why 
does  the  bubble,  resting  upon  the  blue  drop,  buoy  both  to  the  surface 
of  the  kerosene,  except  for  some  molecular  attraction  between  blue 
drop  and  bubble?  Where  this  attraction  is  manifested,  even  slightly, 
it  is  helped  by  the  static  pressure  of  the  liquid  medium  in  which  the 
flotation  takes  place. 

The  great  unsolved  problem  in  flotation  is  the  identity  of  the 
forces  that  do  the  floating.  Some  say  that  it  is  surface  tension,  some 
electricity,  and  some  molecular  attraction  between  the  air-bubbles  and 
the  metallic  particles;  and  there  is  always  the  mystery  as  to  exactly 
the  part  played  by  the  oil.  In  this  article  it  is  intended  to  show  that 


MOLECULAR  FORCES  IN  FLOTATION — SURFACE  COMPRESSION          317 

there  are  certain  molecular  attractions  between  widely  different  sub- 
stances which  would  seem  to  be  nothing  more  or  less  than  the  force  of 
cohesion  acting  at  sensible  distances,  but  for  the  circumstance  that 
such  an  interpretation  runs  counter  to  our  pre-conceived  opinions  as 
to  molecular  attractions;  but  these  attractions  are  shown  in  this 
article  to  exist  between  glass  and  oil,  between  glass  and  water,  directly 
and  through  an  intervening  film  of  oil,  between  glass  and  air,  and 
between  water  and  air.  The  impression  remains  that  a  thorough 
examination  of  our  pre-conceived  opinions  may  show  that  they  are 
fallacious. 

There  are  strong  reasons  for  believing  that  the  state  of  science 
today  is  not  unlike  that  of  learning  at  the  end  of  the  12th  century, 
at  the  time  of  the  great  awakening,  when  the  world  dropped  the 
scholasticism  of  Rome  and  went  back  to  the  philosophy  of  ancient 
Greece.  We  have  lost  the  faculty  of  studying  phenomena,  we  are 
ignorant  of  the  first  principles  of  logic,  and  we  have  degenerated  into 
mere  juggling  with  names. 

Proof  of- this  indictment  is  found  in  Vol.  XXIV  of  the  Encyclo- 
pcedia  Britannica,  at  page  401-2,  where  it  is  stated  that  the  passage  of 
electricity  through  liquids  had  been  explained  as  a  transference  of 
a  succession  of  electric  charges  carried  by  moving  particles  of  matter 
or  'ions.'  Then  it  was  discovered  that  the  moving  particles  that 
carried  the  electric  current  were  much  smaller  than  the  atoms  of 
hydrogen,  and  they  were  re-named  '  corpuscles. '  They  enter  into  the 
structure  of  all  matter.  The  only  known  properties  of  these  corpuscles 
are  their  mass  and  their  electric  charge.  There  is  reason  to  believe 
that  the  whole  apparent  mass  is  an  effect  of  the  electric  charge.  ' '  The 
idea  of  a  material  particle  thus  disappears  and  the  corpuscle  becomes 
an  isolated  unit  of  electricity — an  electron."  This  is  a  typical  'scien- 
tific explanation.'  It  starts  out  inventing  the  word  'ion',  which  it 
immediately  re-christens  'corpuscle'  and  then  'electron,'  and  the  only 
meaning  that  can  be  extracted  from  the  argument  is  that  electricity 
is  supposed  to  be  made  up  of  units,  a  purely  gratuitous  assumption. 
Here  is  another  on  the  same  page  402 :  "Maxwell  and  Hertz  showed 
that  the  velocity  of  propagation  of  light  and  electro-magnetic  waves 
was  identical  and  that  their  other  properties  differed  only  in  degree. 
Thus  light  becomes  an  electro-magnetic  phenomenon.  But  light  is 
started  by  some  form  of  atomic  vibration  and  to  start  an  electro- 
magnetic wave  requires  a  moving  electric  charge."  Here  are  three 
sentences  all  fallacious. 

The  peculiar  tendency  of  the  human  mind  which  substitutes  empty 


318  THE  FLOTATION  PROCESS 

names  for  real  phenomena  and  then  plays  with  the  names  is  the  same 
that  makes  religious  peoples  worship  idols  instead  of  fixing  their 
minds  on  principles.  It  is  easier.  A  pilgrimage  to  a  shrine  where  one 
may  worship  a  rag,  a  bone,  or  a  hank  of  hair,  and  be  absolved,  is  less 
trouble  than  leading  an  exemplary  life.  So  that  when  the  question 
is  asked  "Why  does  a  drop  of  water  that  falls  upon  dust  take  the 
form  of  a  sphere?"  it  is  easier  to  say  "Oh,  surface  tension"  and  let 
it  go  at  that  than  to  think  about  it.  It  is  all  very  well  to  say  that  a 
snark  is  a  boojum,  if  you  first  define  your  boojum;  but  when  you 
scratch  the  boojum  and  find  the  same  old  snark  the  pursuit  of  knowl- 
edge seems  in  vain. 


FLOTATION-TESTS   IN   SEPARATING   FUNNEL 

EFFECT  OF  ALKALINITY. 
(From  the  Mining  and  Scientific  Press  of  January  8,  1916) 

100  grams  of  200-mesh  mill-heads,  assaying  Au  0.17,  Ag  29.53, 
frothed  6  times  in  400  cc.  mill-water,  with  0.44  Ib.  S.  S.  oil  and 
0.44  Ib.  cresylic  acid  per  ton  of  ore,  at  a  temperature  of  80°  F. 

Lime,  Ib.  per  ton 
Test       At  At  ^-Concentrate-Assay-^         r-Tailing-Assay-^ 

Acid 


No. 

start. 

end. 

Gm. 

Au. 

Ag. 

Au. 

Ag. 

1. 

0.08 

0.02 

Acid 

17.562 

0.46 

90.0 

0.12 

16.1 

2. 

0.01 

Neutral 

15.859 

0.60 

110.6 

0.10 

12.4 

3. 

0.15 

" 

15.350 

0.82 

164.6 

0.06 

5.1 

4. 

0.25 

0.01 

Alk. 

13.470 

1.00 

192.1 

0.06 

4.1 

5. 

0.34 

0.02 

« 

14.20 

0.85 

184.2 

0.06 

3.8 

6. 

0.43 

0.04 

« 

15.05 

1.00 

166.4 

0.06 

4.9 

7. 

0.70 

0.12 

" 

26.95 

0.52 

89.3 

0.03 

6.4 

8. 

1.00 

0.25 

" 

31.55 

0.34 

60.3 

0.09 

12.9  . 

In  separatory-funnel  tests,  assays  of  concentrate  are  much  lower 
than  in  plant-practice.  Tailing-assays  are  practically  the  same. 

When  frothing  in  mill-water,  the  best  alkalinity,  both  as  regards 
extraction  and  grade  of  concentrate,  is  from  0.01  to  0.02  Ib.  per 
ton  of  water. 


FLOTATION    PRINCIPLES  319 

FLOTATION   PRINCIPLES 

By  C.  TERRY  DURELL 
(From  the  Mining  and  Scientific  Press  of  February  19,  1916) 

In  attempting  to  start  a  discussion  on  flotation  by  setting  forth 
my  osmotic  hypothesis,  the  main  objects  were  (1)  to  firmly  establish 
fundamental  laws  and  definitions  and  (2)  to  bring  out  and  classify 
new  phenomena.  Flotation  terms  have  been  misused  and  jumbled 
in  the  same  way  that  the  so-called  expert  makes  a  mining  report 
ridiculous  by  the  use  of  geological  terms.  Litigation  has  made  the 
subject  more  confusing,  and  it  is  still  an  indefinite  cloud  to  most 
people.  Now  that  first  principles  and  definitions  are  being  agreed 
upon,  concerted  effort  is  starting  experimentation  along  definite 
lines  that  will  lead  to  far-reaching  results  instead  of  the  heretofore 
duplication  of  efforts  leading  to  nothing.  Before  the  final  solution 
of  a  problem  can  be  accomplished,  the  problem  must  be  stated 
properly.  It  is  therefore  quite  gratifying  to  see  that  the  discussion 
is  fulfilling  the  two  main  purposes  and  that  the  flotation  problem 
now  stands  out  more  clearly. 

A  man  can  never  learn  from  one  who  agrees  with  him  entirely. 
For  this  reason  I  was  pleased  to  see  exceptions  taken  to  my  article 
'Why  Is  Flotation?'  0.  C.  Ralston  thinks  I  used  rather  loosely  the 
two  words  'nascent'  and  'occlusion.'  It  took  me  a  long  time  to 
realize  the  prime  essential  for  an  effective  froth.  This  can  only  be 
described  clearly  by  the  word  '  nascent. '  It  also  required  several 
years  of  patient  effort  to  convince  myself  that  the  whole  subject 
depends  on  gas  'occlusion.' 

Being  unable  to  learn  anything  more  in  this  country  concerning 
flotation,  some  four  years  ago  I  made  a  trip  to  Australia,  the  home 
of  flotation.  There  I  saw  for  the  first  time  copper  concentrate  won 
by  flotation.  At  the  Lake  View  Consols,  in  the  Kalgoorlie  district,  I 
saw  one  of  the  old  bulk-oil  flotation  plants. 

It  was  at  Broken  Hill,  however,  that  I  had  plenty  of  time  and 
opportunity  to  study  flotation.  Companies  using  different  processes 
were  naturally  adverse  to  entertaining  a  stranger  who  might  be 
gathering  information  to  be  used  against  them  in  one  of  the  various 
law-suits.  As  soon  as  the  managers  or  officials  in  charge  were  assured 
that  I  was  not  there  for  that  purpose,  they  afforded  me  ample  oppor- 
tunity to  learn  everything  concerning  flotation,  giving  me  access  to 
figures  and  data.  In  this  country,  it  is  seldom  that  a  comparative 


320  THE  FLOTATION  PROCESS 

stranger  receives  such  courteous  treatment  as  was  shown  me  by 
the  cordial  company  officials  there. 

At  the  Proprietary  mine,  where  the  Delprat  process  was  in 
operation,  no  oil  was  being  used,  yet  there  was  practically  the  same 
persistent  froth  as  at  other  plants  using  the  Minerals  Separation 
process.  This  fact  then  eliminates  the  two  hypotheses  for  flotation 
advanced  by  Mr.  Ralston1,  who  says  that  "The  first  hypothesis  is 
based  on  some  academic  work  done  by  Reinders,  who  deduced  the 
following  inequalities  as  applying  to  a  case  where  a  powder,  or 
the  particles  of  a  colloid,  is  suspended  in  a  liquid  to  which  is  added 
a  second  liquid  that  is  immiscible  with  the  first. "  There  at  the 
Proprietary  mine,  where  500  tons  per  day  was  being  treated  by  a 
single  'cell/  no  such  liquid  was  used.  Therefore,  according  to 
Mr.  Ralston 's  hypothesis,  froth-flotation  could  not  take  place.  Yet 
the  records  show  that  thousands  of  tons  of  zinc  concentrate  has  been 
recovered  by  froth  where  no  oil  was  used.  I  quite  agree  with 
Mr.  Ralston  when  he  says  "It  hardly  needs  to  be  said  that  here  we 
find  something  very  close  to  the  conditions  obtained  in  the  flotation 
process/'  "In  fact,  the  old  Elmore  bulk-oil  flotation  method  fulfills 
exactly  the  conditions  that  Reinders  had  in  mind."  By  basing  the 
whole  subject  of  flotation  on  gas  occlusion,  as  I  have  done  in  my 
article,  '"Why  Is  Flotation?'  in  the  Mining  and  Scientific  Press  of 
September  18,  all  flotation  processes  may  readily  be  explained. 

On  seeing  for  the  first  time  a  single  spitzkasten  being  fed  700  Ib. 
of  ore  per  minute  by  means  of  a  'push-feeder'  as  is  done  at  the 
Proprietary,  one  can  but  marvel  at  the  simplicity  and  rapidity  of 
action  of  this  froth-flotation  process,  which  makes  a  marketable  zinc 
concentrate  with  high  recovery  without  re-treating.  As  no  oil  was 
used,  I  summed  up  as  follows  the  essential  elements:  gas,  acid,  and 
heat,  in  addition  to  ore  and  water.  There  is  nothing  else  essential 
to  this  treatment.  Studying  the  conditions  there,  I  soon  became 
convinced  that  the  function  of  the  acid  was  not  only  to  produce 
bubbles  for  froth-formation,  but  also  for  the  creation  of  selective 
action.  Since  the  solution  was  kept  as  near  the  critical  temperature 
of  80° C.  as  possible,  no  air  from  the  solution  could  aid  in  froth-forma- 
tion because  the  solution  was  under  a  hydrostatic  head  and  was  ad- 
mitted at  the  bottom  of  the  spitzkasten  instead  of  by  means  of  a  jet 
above  the  surface.  It  was  easily  seen  that  the  function  of  gas  was  for 
froth-formation  and  that  the  persistence  of  the  bubbles  was  mainly 
due  to  the  enveloping  net  of  mineral  particles.  What  then  was  the 


i'Why  Do  Minerals  Float?'  by  O.  C.  Ralston,  M.  &  8.  P.,  Oct.  23,  1915. 


FLOTATION    PRINCIPLES  321 

function  of  the  heat?  The  cold  ore  dropping  into  this  hot  solution 
carried  some  air  with  it  which  the  heat  expelled.  This  was  not  the 
essential  factor.  The  heat  expelled  enough  of  the  occluded  gas  from 
the  ore  particles  to  form  nuclei  for  the  attachment  of  nascent  gas  to 
form  flotation  bubbles. 

Studying  the  Elmore  vacuum  process  at  the  British  Broken  Hill 
plant  at  a  later  date,  I  summed  up  the  essential  elements  there  as 
follows:  vacuum  (to  liberate  the  air)  acid,  oil,  and  alkali.  At  a  first 
glance  it  was  seen  that  here  was  another  method  of  making  bubbles 
and  froth.  This  froth  was  perhaps  more  persistent,  as  the  envelope 
for  the  bubbles  seemed  tougher.  The  difference  was  so  slight  that  it 
is  best  described  as  that  between  the  froth  formed  during  the  early 
stage  of  the  clean-up  in  the  acid  or  'cutting-down'  tank  of  a  cyanide 
plant  and  the  froth  formed  during  the  later  stages.  It  was  natural, 
therefore,  to  assume  that  the  principle  or  cause  of  this  Elmore  process 
of  flotation  was  identical  with  that  of  the  Delprat  at  the  Proprietary. 
I  was  told  there,  and  have  been  repeatedly  told  since,  that  the  oil  was 
the  cause  of  the  selective  action.  I  never  will  believe  this,  with  all  the 
evidence  against  it,  although  on  account  of  adsorption — not  occlu- 
sion— of  gases  by  the  ore  particles,  they  are  more  easily  wetted  with  oil 
than  with  water.  The  results  at  these  two  mines  were  practically 
the  same.  The  grade  of  the  concentrate  at  the  British  plant  was 
higher,  by  reason  of  mechanical  refinements,  and  not  the  difference 
in  process.  Therefore  the  oil  could  not  be  the  essential  element  for 
selective  action,  because  no  oil  was  used  at  the  Proprietary.  The  oil 
was  an  essential  element  only  in  that  it  toughened  the  froth.  Owing 
.to  mechanical  means  of  operation,  the  froth  could  not  be  removed 
so  quickly  nor  could  it  be  carried  in  such  a  deep  layer.  Therefore 
oil  was  added  to  toughen  it.  Using  Mr.  Scott's  words2,  "This  froth 
rises  and  floats  much  the  same  as  a  board  would"  while  the  Delprat 
bubbles  "float  over,  if  we  get  them  over  before  they  break";  and 
' '  if  they  do  break,  the  mineral  drops  and  is  caught  by  the  bubbles 
below."  Oil,  then,  can  be  eliminated  in  making  the  following  com- 
parison between  the  essential  elements  of  these  two  processes.  Acid 
creates  the  selective  action  as  in  the  Delprat  method ;  lime  is  then 
added  to  neutralize  it,  because  the  vacuum  machines  are  of  cast-iron. 
Acid  was  found  to  be  necessary  in  the  Delprat  process  to  create  the 
bubbles.  It  was  necessary  for  these  bubbles  to  form  as  they  "came 
into  being"  on  mineral  particles  as  nuclei.  Nascent  bubbles  of  air 


2Walter  A.  Scott,  counsel  for  defendant  in  the  case  of  Minerals  Separa- 
tion v.  Miami. 


322  THE  FLOTATION  PROCESS 

are  formed  in  the  same  way,  so  that  the  vacuum  of  the  Elmore  process 
takes  the  place  of  the  acid  in  the  Delprat. 

At  the  British  plant,  in  making  a  froth,  the  solutions  were  not 
heated,  for  the  reason  that  the  vacuum  which  drew  the  dissolved 
air  from  the  liquid,  in  accordance  with  the  law  of  Henry,  also  drew 
a  sufficiency  of  occluded  air  from  the  mineral  particles  to  form 
nuclei  for  the  air  "coming  into  being"  from  the  liquid.  The  acid 
had  already  acted  as  previously  described.  The  small  slow-speed 
mixer,  just  ahead  of  the  vacuum  machines,  used  for  stirring  oil  into 
the  thickened  pulp,  could  in  no  way  super-saturate  the  mass  with 
air  as  is  the  case  with  a  Minerals  Separation  machine,  which  process 
will  be  taken  up  later. 

When  I  began  the  study  of  the  De  Bavay  process  at  the  Amal- 
gamated Zinc  plant,  I  was  at  a  loss,  at  first,  to  see  how  the  same 
principles  underlying  the  other  two  processes  just  mentioned  could 
apply  there.  The  following  essential  elements  were  separated  out: 
gas  (in  the  form  of  air),  acid,  and  oil.  Mr.  Meredith  told  me  the 
object  of  the  acid  was  to  clean  the  mineral  particles.  While  it 
undoubtedly  does  this,  my  contention  is  that  it  acts  as  an  electrolyte, 
as  I  have  described,  to  create  the  selective  action  afterward  manifest 
during  the  oiling  and  aerating  stages  of  the  process. 

Oiling  of  the  mineral  particles  is  the  next  stage  and  can  only 
take  place  in  liquid  pulp,  as  I  have  explained,  when  particles  them- 
selves contain  gas.  It  required  a  careful  study  of  the  apparatus 
at  the  Amalgamated  plant  before  I  was  able  to  understand  that  the 
same  underlying  principles  applied  here.  Air  was  necessary;  yet 
where  and  how  was  it  introduced?  This  is  best  described  in  T.  J, 
Hoover V  words:  "Throughout  this  manipulation,  including  .the 
acid-washing,  the  oiling,  the  raising  with  compressed  air,  and 
the  flowing  over  the  corrugated  cone,  the  sulphide  particles  are 
repeatedly  aerated,  and  as  a  result,  especially  after  the  oiling,  take 
up  their  adhesive  air-films  and  float."  They  were  not  using 
corrugated  cones  when  I  was  there.  Instead,  the  cones  were  covered 
with  concentric  rows  of  staggered  triangular  obstructions.  These 
were  made  by  bending  the  triangular  burrs  from  holes  punched  in 
galvanized  sheet-iron  cones  until  they  were  perpendicular  to  the 
surface.  These  cones  were  then  fitted  down  tightly  over  similar 
cones  not  punched.  A  montejus  was  used  to  lift  the  prepared  pulp 
to  these  cones.  As  Mr.  Hoover  says,  "The  subjecting  of  the  oil  pulp 


s'Concentrating  Ores  by  Flotation,'  by  Theodore  J.  Hoover.    Second  edition, 
page  117. 


FLOTATION    PRINCIPLES  323 

to  compressed  air  may  be  an  essential  part  of  the  operation."  It 
undoubtedly  is,  and  this  method  is  patented  by  Dudley  H.  Norris,4 
although  opposed  by  Minerals  Separation  Ltd.  when  application  for 
patent  was  made  in  England. 

The  De  Bavay  float  is  caused  by  air.  Why  is  it  not  a  froth? 
Norris  turns  his  super-saturated  liquid  directly  into  the  pulp-mass 
and  a  froth  is  formed.  The  pulp-mass  at  the  Amalgamated  Zinc 
plant,  super-saturated  with  air,  was  turned  on  to  the  top  one  of  each 
series  of  four  cones.  There  was  no  chance  for  froth  to  form  while 
spreading  in  a  thin  stream  over  the  surface  of  a  cone.  This  float, 
however,  is  entirely  different  from  the  unstable  float  on  the  Henry 
Wood  type  of  machine,  which  depends  on  surface  tension  entirely. 
It  is  best  described  in  the  words  quoted  from  De  Bavay:  "When 
the  contents  of  the  receptacle  were  emptied  into  a  beaker,  a  thick 
clean  layer  of  'black-jack'  sprang  to  the  surface  of  the  liquid,  while 
the  white  clean  gangue  was  precipitated  to  the  bottom. '  '5 

Upon  studying  several  plants  using  the  Minerals  Separation 
process,  the  following  essential  elements  of  flotation  were  easily 
recognizable:  air  (beat  in  by  stirrers  to  super-saturation),  acid,  oil, 
and  heat. 

It  is  to  be  noted  that  these  are  the  same  as  described  in  the  other 
processes.  Practically  the  only  difference  is  that  the  froth  is  more 
persistent,  because  there  is  more  slime  with  which  to  armor  the 
bubbles.  The  violent  agitation  coagulates  the  exceedingly  fine  metallic 
particles  in  the  same  way  that  butter  forms  in  a  churn.  These  coagules 
are  then  taken  up  in  the  froth  the  same  as  larger  metallic  particles. 
As  Mr.  Hoover6  states,  "Large  quantities  of  air  are  beaten  into  the 
pulp.  By  running  the  machine  for  a  few  minutes  on  water  alone,  it 
will  be  observed  that  the  quantity  of  air  so  beaten  into  the  pulp  is 
enormous,  for  the  clean  water  will  be  milk-white."  This  air,  as  it 
"comes  into  being,"  uses  the  mineral  particles  as  nuclei  from  which 
to  grow  into  bubbles. 

The  resume  of  these  commercial  processes  is  to  show  that  nascent 
gas  is  necessary.  The  only  explanation  of  single  selective  action  for 
all  processes  is  that  gas  is  held  in  the  solid  particles. 

A  theory  that  will  not  explain  all  of  these  processes  is  of  no  value 
whatever.  Both  of  Mr.  Ralston 's  hypotheses  depend  upon  the  use  of 


4U.  S.  Patent  No.  864,856,  Nov.  19,  1906. 

^'Flotation  in  Australia,'  by  Charles  S.  Galbraith,  M.  &  8.  P.,  July  17, 
1915,  page  85. 

6'Concentrating  Ores  by  Flotation,'  2nd  edition,  page  136. 


324  THE  FLOTATION  PROCESS 

I 

oil,  which  is  not  an  essential  element  to  flotation,  as  was  shown  above. 
Also  these  hypotheses  assume  that  bubbles,  existing  as  such  in  a  liquid 
pulp,  can  then  have  mineral  particles  attached  to  them.  If  this  be  so, 
and  it  is  not  necessary  to  grow,  as  it  were,  the  bubbles  from  the  nascent 
gas  in  the  liquid,  why  is  it  necessary  to  beat  air  into  solution  beyond 
the  saturation  point  as  is  done  in  all  froth-flotation  machines  using 
air  as  an  adjunct  except  in  the  Callow  machine?  It  would  be  much 
simpler  to  turn  in  a  stream  from  a  compressor  or  blower.  If  electrifi- 
cation is  then  all  that  is  needed  to  produce  attachment  of  the  mineral 
particles,  surely  there  are  plenty  of  ways  to  electrify  the  bubbles. 
Thomas  M.  Bains7  says,  "It  would  seem  easier,  therefore,  to  electrify 
a  bubble  than  to  keep  it  from  being  electrified."  No;  something 
more  than  electrification  is  required  of  the  bubble,  as  all  who  have 
tried  to  produce  a  float  in  this  manner  well  know.  James  A.  Block,12 
in  his  criticism  on  my  article,  says :  "I  cannot  see  how  the  water  in  a 
Callow  or  other  pneumatic  machine  can  become  greatly  super-satu- 
rated. "  This  is  best  answered  by  Mr.  Callow8  himself:  "The  bubbles 
composing  the  froth  are  generated  under  a  hydraulic  pressure  varying 
from  15  to  40  in."  It  matters  not  whether  the  water  be  saturated 
"with  air  at  a  pressure  of  several  atmospheres,"  as  was  done  by 
Norris,  or  under  a  hydraulic  pressure  of  15  inches,  because,  as  I 
pointed  out,  it  is  not  the  air  that  is  held  dissolved,  but  it  is  the  air 
that  comes  out,  which  is  available  for  mineral  attachment.  A 
hypothesis  based  on  nascent  and  occluded  gas  explains  all  kinds  of 
flotation  as  well  as  all  flotation  machines. 

More  flotation  experiments  have  been  carried  out  in  Australia  than 
in  any  other  country.  No  publication  of  systematic  experiments 
to  learn  the  reasons  for  flotation  is  so  complete  as  that  in  the 
proceedings  of  the  Royal  Society  of  Victoria,  of  Kenneth  A.  Mickle.9 
His  experiments  (many  of  which  I  have  verified  in  the  laboratories 
of  the  Colorado  School  of  Mines  while  experimenting  in  the  new 
testing  plant  there  some  three  years  ago  with  the  Horwood  process) 
showed  nascent  gas  necessary  and  also  that  the  particles  must 
contain  gas.  He  showed  by  experiments  that  (1)  heat  or  reduction 
of  pressure  to  liberate  gas,  that  (2)  generation  of  gas  by  means  of 
acid,  or  that  (3)  super-saturation  of  solutions  with  gas,  will  cause 


7'The  Electrical  Theory  of  Flotation,'  by  Thomas  M.  Bains,  Jr.,  M.  &  8.  P., 
Nov.  27,  1915,  page  824. 

s'Notes  on  Flotation,'  by  J.  M.  Callow,  M.  &  8.  P.,  Dec.  4,  1915,  page  852. 

»Vol.  XXIII  and  XXIV  (N.  S.),  Part  2,  1911.  Abstracted  in  Eng.  &  Min. 
Jour.,  page  307,  Aug.  12,  1911  (vol.  92),  and  page  71,  July  13,  1912  (vol.  94). 


FLOTATION    PRINCIPLES  325 

minerals  to  float  or  tend  to  float  without  the  aid  of  oil.  He  showed 
the  effect  of  gases  occluded  by  minerals  to  be  (1)  the  particles  are 
not  wholly  wetted  when  immersed  in  water;  (2)  the  particles  tend 
to  float  when  sprinkled  on  water;  (3)  the  particles  when  immersed 
collect  bubbles  as  the  solution  is  heated  or  exposed  to  vacuum  and 
float  or  tend  to  float;  and  (4)  the  particles  in  gas-saturated  solutions 
collect  the  bubbles  evolved.  He  says,  "In  my  earlier  paper,  it  was 
shown  that  mineral  particles  absorb  gases  to  an  extent  not  previously 
suspected  and  that  they  retain  the  gas  adsorptions  with  such 
persistency  that  they  could  neither  be  easily  separated  by  mechanical 
means  nor  much  affected  by  gravity  and  gas  expansion."  He 
also  says,  "In  previous  investigations,  I  found  that  carbon  dioxide 
was  obtained  from  all  sulphides  by  the  aid  of  heat  and  exhaustion 
in  the  presence  of  water.  It  is  probable  that  the  gas  film  can  be 
expanded  for  removal  in  appreciable  quantities  only  in  the  presence 
of  water  and  that  exhaustion  in  the  dry  state  does  not  remove  all 
the  gas  present." 

With  a  view  to  further  investigating  the  gas  held  by  solids,  he 
conducted  the  following  experiments: 

1.  Copper  and  silver  foil  were  cleaned  with  sodium   hydrate 
and  distilled  water  and  dried.     These  and  uncleaned  pieces  were 
treated  in  a  vacuum-flask.    Few  bubbles  formed  on  cleaned  foil  with 
distilled  and  air-free  distilled  water,  but  more  on  the  uncleaned. 
All  foil  floated  in  tap-water. 

2.  Six  steel  needles  were  cleaned  in  the  same  way  as  the  foil 
and  allowed  to  stand  one  half -hour  in  alcohol  and  then  dried  in  a 
desiccator.     They  would  not  float  on  distilled  water  until  it  had 
been   exposed   for  some   time   to  the   air.     Another   set   of  needles 
and  iron   wire  were   similarly   cleaned,   but  would  not  float   until 
allowed  to  stand  in  a  desiccator  for  two  days.     The  same  results 
were  obtained  with  sulphides  cleaned  with  sulphuric  acid. 

"These  experiments  show  that  perfectly  cleaned  needles  and 
iron  wire  will  float  on  the  surface  under  the  following  conditions: 
(a)  if  the  water  is  allowed  to  stand  for  some  time  in  contact  with 
air;  (b)  if  the  needles  and  wire  are  allowed  to  remain  exposed  to 
the  air  for  sufficient  time." 

3.  Cleaned  and  uncleaned  pieces  of  iron  wire,  on  being  immersed 
in   a   saturated   solution   of  carbon   dioxide,   showed   the  •  following 
results:    (a)    clean   pieces   collected   very   few   bubbles,   while    (b) 
unclean  pieces  were  covered  with  a  frost  of  bubbles. 

I  have  confirmed  these  experiments,  therefore  I  am  positive  of 


326  THE  FLOTATION  PROCESS 

the  incorrectness  of  Mr.  Rickard's  statement,  "If  you  place  an 
ordinary  needle,  say,  a  lace  needle  suitable  for  use  with  No.  80  thread, 
on  the  surface  of  a  bowl  of  water,  it  sinks  at  once  to  the  bottom, 
in  obedience  to  the  law  of  gravity.  If,  however,  you  pass  the  needle 
through  your  hair,  so  that  it  becomes  greased,  it  will  float  on  the 
water. ' >10  This  is  the  same  old  false  assumption  that  oil  is  a  necessity 
instead  of  an  aid  to  flotation. 

Swinburne  and  Eudorf11  say,  "A  way  of  demonstrating  the 
presence  of  gaseous  envelopes  is  to  sift  some  powdered  substance 
which  easily  sinks,  such  as  sand  or  ferrous  sulphides,  upon  the 
surface  of  hot  water,  previously  freed  from  gas  by  boiling.  Bubbles 
of  gas  rise  from  the  surface  of  solid  particles."  "It  seems  necessary 
that  the  gas  should  be  produced  at  the  surface  of  the  particles 
themselves."  The  air-film  always  plays  an  important  part;  and 
if  the  ore  is  thoroughly  washed  or  boiled  in  water  to  remove  the 
air-film,  it  cannot  be  concentrated  with  acid." 

There  are  many  other  references  all  showing  the  same  thing: 
that  the  mineral  particles  to  be  floated  must  contain  gas  so  as  to 
act  as  nuclei  for  the  gas  as  it  "comes  into  being"  from  the  liquid. 
Therefore,  in  my  former  article,  I  did  not  present  this  evidence  to 
prove  my  statement,  which  seemed  a  self-evident  fact  in  view  of  the 
present  knowledge  of  the  subject. 

Mickle  collected  gases  from  concentrate  made  from  Broken  Hill 
material  some  of  which  gas  contained: 

(1)  (2) 

N    72%  N    82% 

O   2  O   2 

C02   26  C02   16 

It  is  seen  that  these  gases  obey  Henry's  law,  each  existing 
independent  of  the  others  and  not  displacing  the  others  as 
Mr.  Block12  says  undoubtedly  would  be  the  case.  An  analysis  of 
a  sample  from  the  Horwood  process  gave: 

N    95% 

O    1 

C02    4 

These  three  samples  of  gas  became  disengaged  from  three  samples 


io'What  Is  Flotation?'  by  T.  A.  Rickard,  M.  &  8.  P.,  Sept.  11,  1915,  page  384. 
uPaper  read  before  the  Faraday  Society,  Dec.  12,  1905,  by  J.  Swinburne 
and  G.  Rudorf.    Abstracted  in  En@.  &  Min.  Jour.,  Feb.  10,  1906. 
i2James  A.  Block,  M.  &  8.  P.,  Oct.  30,  1915,  page  659. 


FLOTATION    PRINCIPLES  327 

of  concentrate  which  were  allowed  to  stand.  Afterward  a  vacuum 
applied  to  No.  1  sample  (70  gm.  sulphide)  gave  a  further  amount 
of  1.7  cc.  gas  analyzing: 

N    27% 

O     14.1 

C02     58.8 

On  raising  the  temperature  to  the  boiling  point  and  subjecting 
this  sample  to  vacuum,  there  was  then  given  off  8.9  cc.  of  gas, 
which  was  found  to  be  practically  all  carbon  dioxide. 

From  the  No.  2  sample  he  obtained  18.5  cc.  gas  of  which 
practically  all  was  C02.  On  subjecting  minerals  to  reduced  pressure 
and  heat,  he  found  that  he  could  obtain  more  gas  from  calcite  and 
quartz.  This  was  mostly  C02.  He  proved  in  all  these  cases  that 
the  C02  obtained  was  not  from  the  decomposition  of  carbonates.  This 
shows  that  minerals  in  general  occlude  gas,  although  Mr.  Ralston1 
says  that  "good  cases  of  occlusion  have  been  found  thus  far  only 
in  amorphous  substances."  Mr.  Block  is  quite  ri^it  when  he  says 
"that  it  would  be  liberated  with  sufficient  rapidity  to  float  the 
particles  does  not  seem  probable."12  Also  Mr.  Ralston1  is  correct 
in  saying  "How  the  tightly-held  gas  could  be  liberated  fast  enough 
to  compare  with  the  exceedingly  short  time  which  it  takes  to  accom- 
plish flotation  of  a  sulphide  particle  is  difficult  to  explain  physically. ' ' 
I  simply  stated  that  "if  this  gas  be  expelled  from  them,  when  they 
are  in  a  liquid,  at  a  time  when  the  gas  is  expelled  from  the  liquid, 
they  become  the  nuclei  for  the  formation  of  gas  bubbles."  On  the 
other  hand,  if  bubbles  are  not  formed  from  nascent  gas  of  the 
liquid  in  contact  with  the  mineral  particle  there  can  be  no  adhesion 
because  the  bubbles  are  surrounded  by  liquid  films;  or,  if  the 
particles  contain  no  occluded  gas,  there  can  be  no  adhesion  because 
the  particles  are  surrounded  by  liquid  films. 

That  these  two  words  'nascent'  and  'occlusion'  were  objected  to 
shows  the  necessity  of  extreme  care  in  the  choice  of  terms,  and  I 
am  glad  that  Mr.  Ralston  brought  up  this  point.  'Nascent'  is 
defined  in  Webster's  New  International  distionary  (3rd),  1915,  as 
follows:  "Being  born;  coming  into  existence;  beginning  to  grow; 
commencing,  or  in  process  of,  development. ' '  The  Century  dictionary, 
5th  edition,  1911,  gives  practically  the  same  definition  as  follows: 
"Beginning  to  exist  or  to  grow;  commencing  development;  coming 
into  being;  incipient."  The  following  usage  is  given:  "Wiping 
away  the  nascent  moisture  from  my  brow:  Barham,  'Ingoldsby 
Legends'."  Available  gas  of  any  kind  for  flotation  must  "come 


328  THE  FLOTATION  PROCESS 

into  being"  in  this  way.  Mr.  Bains13  excellently  describes  this,  as 
follows:  "If  powdered  galena  ore,  with  a  limestone  gangue,  be 
dropped  into  pure  water,  most  of  the  powder  will  immediately  sink 
to  the  bottom.  As  the  air  enclosed  by  the  particles  is  expelled 
gradually,  one  sees  the  formation  of  'armored'  bubbles,  some  of 
which  may  last  for  days.  Here  is  flotation  without  oil  or  acid.  If 
nitric  acid  be  added,  the  gas  bubbles  formed  by  the  action  of  the 
acid  on  the  gangue  will  carry  up  particles  of  galena."  I  have 
placed  £-inch  pieces  of  quartz,  galena,  and  other  minerals  in  a 
beaker  filled  with  water  saturated  with  air  at  atmospheric  pressure. 
The  purpose  was  to  watch  the  formation  of  the  bubbles.  More  small 
bubbles  formed  on  the  metallic  minerals  when  heat  was  applied. 
The  bubbles  formed  on  all  minerals  apparently  in  the  same  way 
that  moisture  forms  on  one's  brow.  I  wish  to  describe  this.  There 
is  only  one  single  word  in  the  English  language  that  can  be  used 
to  do  it — 'nascent.'  This  is  not  "the  dissolved  gas  that  can  be 
liberated,"  but  it  is  the  dissolved  gas  at  the  instant  of  liberation. 

Eegarding  occlusion,  Mr.  Ealston  has  been  kind  enough  to  men- 
tion three  ways  by  which  gases  can  be  held  in  solids,  and  I  should 
have  used  more  care  in  the  choice  of  these  terms.  I  used  the 
word  'occluded'  as  a  general  term  to  denote  either  surface  adsorption 
or  solid  solution.  As  Mr.  Ralston  says,  "this  is  a  term  the  meaning 
of  which  has  been  much  disputed."  Trying  to  show  that  the  gas 
in  the  mineral  obeys  the  same  laws  as  the  gas  in  the  liquid,  as 
proved  by  Mickle,  I  spoke  of  the  gas  being  dissolved  in  the  solid 
and  thus  led  up  to  the  term  'occlusion,'  having  in  mind  the 
following:  "The  amount  of  gas  which  dissolves  in  a  given  quantity 
of  water  is  proportional  to  the  pressure,  and  from  this  experimental 
result,  Van't  Hoff  showed  mathematically  by  the  principle  of  thermo- 
dynamics that,  when  in  solution,  this  same  gas  must  exert  an  osmotic 
pressure";14  and  that  "Substances  dissolved  by  solids  have  an  osmotic 
pressure  as  shown  by  Van't  Hoff,  so  we  can  speak  of  solid  solu- 
tions";15 also  that  "the  greater  the  pressure  to  which  the  gas  is 
subjected,  the  larger  the  quantity  which  will  be  adsorbed  by  the 
solid."16 

Viscosity   is   another   word   that   has   been   incorrectly   used   in 


Electrical  Theory  of  Flotation,'  by  Thomas  M.  Bains,  M.  &  S.  P., 
Nov.  27,  1915,  page  824. 

n'The  Recent  Development  of  Physical  Science,'  by  W.  C.  Dampier 
Whetham,  page  113,  2nd  edition,  1904. 

15'Zeit.  Phys.  Chem.,'  1890,  5,  322. 

le'Elements  of  Physical  Chemistry,'  by  Harry  C.  Jones,  1902,  page  267. 


FLOTATION   PRINCIPLES  329 

connection  with  flotation.  Mr.  Rickard10  in  his  article,  'What  is 
Flotation?'  states:  "The  combination  of  low  tension  and  high 
viscosity  enables  a  bubble  of  gas,  rising  through  the  liquid,  to  lift 
the  surface  film  of  the  liquid,  which  the  tension  of  the  bubble-film 
is  not  strong  enough  to  break,  so  the  bubble  endures";  and  cites 
'A  Text  Book  of  the  Principles  of  Physics,'  by  Alfred  Danniell, 
1911.  Also  Mr.  Rickard  states:  "Pure  water  has  great  surface 
tension,  it  also  has  no  superficial  viscosity." 

Viscosity  as  known  today  is  an  entirely  different  property  of 
matter  from  that  which  Danniell  in  1885  confused  with  surface 
tension. 

Perhaps  the  best  definition  of  viscosity  is  by  Harry  C.  Jones,17 
as  follows:  "We  need  simply  mention  here  the  works  of  Poisenille, 
Pagliani  and  Battelli,  Slotte,  Gartenmeister,  and  Traube"  *  *  * 
"The  monumental  works  of  Thorpe  &  Rodger  merit  more  careful 
attention."  *  *  *  "They  prove  conclusively,  what  has  been  hinted 
at  before,  that  *  *  *  viscosity  may  be  taken  as  the  sum  of  the 
attractive  forces  in  play  between  the  molecules;  *  *  *  It  is,  there- 
fore, made  evident  that  viscosity  or  inter-molecular  attraction  is 
in  reality  a  property  of  the  atoms  of  which  the  molecules  are 
composed."  This  'superficial  viscosity'  is  well  explained  in  the 
Encyclopedia  Britannica,18  as  follows:  "The  varying  of  contami- 
nation to  which  a  water  surface  is  subject  are  the  causes  of  many 
curious  phenomena.  Among  these  is  the  'superficial  viscosity'  of 
Plateau."  "*  *  *  "Plateau  attributes  these  differences  to  a  special 
quality  of  the  liquids  named  by  him  'superficial  viscosity.'  It  has 
been  proved,  however,  that  the  question  is  one  of  contamination 
and  that  a  water  surface  may  be  prepared  so  as  to  behave  in  the 
same  manner  as  alcohol."  Mr.  Rickard,  in  his  second  article,  page 
517,  Mining  and  Scientific  Press,  October  2,  1915,  says:  "To  make 
bubbles,  the  surface  tension  of  water  in  the  flotation-cell  must  be 
decreased  by  a  contaminant  and  at  the  same  time  the  viscosity 
of  the  liquid  must  be  strengthened."  As  shown  above,  it  is  not 
the  viscosity  but  the  general  surface  tension  effect  that  must  be 
strengthened.  As  I  pointed  out,  a  soluble  or  partly  soluble  oil  will 
decrease  the  surface  tension  of  water  because  it  dilutes  the  water, 
which  has  the  greater  surface  tension.  By  reason  of  this  cause 
alone,  the  tendency  to  float  is  decreased  and  the  bubbles  burst 


^'Conductivity  and  Viscosity  in  Mixed  Solvents,'  Carnegie  Institute,  Publi- 
cation No.  80,  1907,  page  19. 

edition,  under  'Capillary  Action.' 


330  THE  FLOTATION  PROCESS 

more  easily.  Using  a  volatile  oil  in  a  M.  S.  machine,  I  have  had 
the  bubbles  burst  so  violently  that  the  cement  floor  was  blackened 
with  zinc  sulphide  at  a  distance  of  several  feet  from  the  machine. 
At  the  same  time  I  was  making  a  very  clean  zinc  concentrate  from 
Leadville  mixed  sulphides  after  a  Horwood  roast.  As  no  other 
contaminant  was  used,  this  was  only  made  possible  by  having  the 
mineral  particles  well  oiled  with  the  thinnest  possible  film  to  aid 
cohesion  in  armoring  the  bubbles  well  with  the  zinc  sulphide  particles. 
In  this  case  the  surface  tension  was  still  further  reduced  by  the 
sulphuric-acid  electrolyte. 

Most  oils,  however,  aid  modern  flotation  in  three  ways,  as  I  tried 
to  point  out  in  my  former  article,  by  (1)  decreasing  the  force 
of  adhesion  of  water  for  mineral  particles  by  forming  films  around 
them,  (2)  increasing  the  cohesive  force  of  the  mineral  particles  for 
each  other  to  aid  in  the  formation  of  a  network  of  mineral  particles 
around  the  bubbles  to  toughen  them,  and  (3)  toughening  the  bubbles 
by  forming  films  of  oil  around  the  bubbles  in  addition  to  those  of 
the  water.  'Toughen*  is  not  a  good  word  whereby  to  express  the 
meaning.  Mr.  Ralston  explains  this  very  well  and  at  length  on 
page  624,  Mining  and  Scientific  Press  of  October  23,  1915,  under 
his  inter-facial  tension  hypothesis.  He  claims,  however,  "It  is 
doubtful  if  the  air  bubbles  could  be  completely  mantled  by  oil." 
This  is  contrary  to  the  experience  of  others.  The  colors  on  the 
bubbles  indicate  that  they  are  man  tied. "  This  shows  that  Mr. 
Callow  is  right  when  he  says  "The  bubble-mantles  in  a  flotation- 
machine  are  undoubtedly  composed  of  oil,  or  oil  emulsion."19  The 
sum  of  these  tension  effects  causes  persistent  bubbles,  even  though 
the  surface  tension  of  the  water  has  been  reduced.  These 
undoubtedly  are  extremely  thin  films,  at  least  approaching  one 
molecule  in  thickness. 

Therefore  molecular  forces  must  be  taken  into  account  in  dealing 
with  them;  as  Mr.  Ralston  says,  "The  underlying  cause  of  the 
tensions  and  of  electric  charges  is  the  same  thing — some  strange 
molecular,  atomic,  or  other  force  manifested  in  'adhesion,'  'cohesion/ 
or  even  'gravitation/  if  you  please."  In  dealing  with  these  inter- 
facial  tensions,  the  drop-weight  method  cited  by  Mr.  Coghill20  for 
determining  surface  tension  is  of  no  value  to  flotation. 

The  inter-facial  hypothesis  of  Mr.  Ralston  explains  very  well 
indeed  the  persistency  of  bubbles,  but  I  am  not  so  easily  satisfied 


lo'Notes  on  Flotation,'  by  J.  M.  Callow,  M.  d  S.  P.,  Dec.  4,  1915,  page  854. 
so'Surface  Tension,'  by  Will  H.  Coghill,  M.  &  8.  P.,  Oct.  9,  1915,  page  543. 


FLOTATION    PRINCIPLES  331 

as  is  Mr.  Block,13  who  says,  "T.  J.  Hoover,  for  instance,  in  his 
book,  'Concentrating  Ores  by  Flotation/  presents  a  consistent 
theory."  Mr.  Hoover  (2nd  edition,  page  72)  says:  "There  has 
been  no  satisfactory  theory  yet  propounded  as  to  why  acid  does 
promote  the  preferential  adhesion  of  water  to  gangue  particles." 
Even  the  late  electrical  theory  fails  to  answer  all  the  questions 
asked  by  Mr.  Hoover,  on  page  100  of  his  book.  I  answered  the 
above  question  in  my  article  by  showing  that  an  acid  or  any  electro- 
lyte creates  osmotic  pressure,  by  trying  to  enter  the  solid  particles, 
of  which  their  surfaces  act  as  septums.  If  this  pressure  be  sufficient 
to  drive  most  of  the  gas  out  from  the  gangue  particles,  the  metallic 
particles  can  be  floated,  for  the  reason  that  there  is  still  left  sufficient 
gas  in  them  to  become  nuclei  for  bubble  formation  by  the  nascent 
gas  of  the  liquid. 

As  shown  by  Mickle's  experiments,  mentioned  above,  there  is 
more  gas  in  sulphides  than  in  other  minerals  and  it  is  held  more 
persistently  in  the  sulphides.  Thus  a  selective  flotation  is  created. 
I  have  confirmed  these  tests. 

Everyone  who  has  experimented  with  flotation  has  seen  how 
too  much  acid  will  'kill*  the  float.  That  is,  the  greater  osmotic 
pressure  drives  the  air  from  the  metallic  particles  as  well  as  from 
the  gangue  particles. 

This  effect  is  not  to  be  confused  with  that  caused  by  substances 
such  as  tannin  or  saponin  mentioned  by  Mr.  Callow19  as  colloidal 
impurities  or  volatile  oils  and  the  like,  which  destroy  bubbles  by 
reducing  the  surface  tension  to  the  extent  that  the  gas  pressure 
from  within  breaks  or  even  explodes  them.  This  weakening  of  the 
surface  tension  by  a  colloid  is  an  entirely  different  phenomenon  from 
that  shown  when  the  osmotic  pressure  is  increased  by  a  crystalloid. 

"The  crystalloids  when  dissolved  in  water  change  in  a  marked 
degree  its  properties;  for  example,  they  dimmish  the  vapor  pressure, 
lower  the  freezing  point,  and  reduce  the  boiling  point."21 

And  as  Dr.  Lupke22  states,  the  four  laws  in  speaking  of  dilute 
solutions,  are  "  Equimolecular  solutions  of  any  substances,  prepared 
by  using  equal  weights  of  the  same  solvent,  exhibit  equal  osmotic 
pressure,  equal  relative  depressions  of  vapour-pressure,  equal  risings 
of  boiling  point,  and  equal  lowerings  of  freezing  point." 


si'Text  Book  of  Physics,'  by  J.  H.  Poynting  &  J.  J.  Thompson,  3rd  edition, 
1905,  page  186. 

22'The  Elements  of  Electro-Chemistry,'  by  Robert  Lupke,  2nd  edition,  1903, 
page  119. 


332  THE  FLOTATION  PROCESS 

In  maintaining  that  osmotic  pressure  of  an  electrolyte  is  the 
cause  of  selective  flotation,  it  is  well  to  look  into  the  motive  power 
of  osmosis.  Kahlenberg23  states  it  "lies  in  the  specific  attractions 
or  affinities  between  the  liquids  used  and  also  between  the  latter 
and  the  septum  employed.  These  affinities  have  also  at  times  been 
termed  the  potential  energy  of  solution,  etc.;  they  are,  to  my  mind, 
essentially  the  same  as  what  is  termed  'chemical  affinity'."  Or, 
as  F.  H.  Garrison24  put  Taube's  theory:  "The  driving  force  in 
osmosis  is  a  superficial  (or  inter-facial)  pressure  obtained  by  sub- 
tracting the  surface  tension  of  one  fluid  from  the  tension  of  the 
fluid  into  which  it  diffuses."  Or  again  as  Van't  Hoff  and  his 
followers  contend  "The  molecules  of  a  dissolved  substance  exert  the 
same  pressure  against  a  semi-permeable  membrane,  during  osmotic 
processes,  as  they  would  exert  against  the  walls  of  an  ordinary  vessel 
were  they  in  the  gaseous  state  at  the  same  temperature  and  the  same 
concentration."22  Since  these  authorities  do  not  agree  on  the  motive 
force  of  osmosis,  investigation  must  rest  for  want  of  further  data. 

However,  all  theories  of  flotation,  be  they  electrical  or  otherwise, 
must  come  to  osmosis  for  their  solution.  This  is  not  to  question 
the  fact  shown  by  electrolysis  that  every  atom  of  matter  is  capable 
of  uniting  with  a  definite  quantity  of  electricity.  Nor  is  it  to  question 
that  corpuscles  (later  termed  electrons  by  Dr.  Stoney)  do  not  revolve 
around  atoms  which  are  thousands  of  times  larger.  But  it  is  to 
question  any  hypothesis  that  does  not  take  into  account  the  fact 
that  particles  will  not  float  when  all  the  gas  is  driven  from  them. 
Osmotic  pressure  can  free  particles  of  their  occluded  gas.  Whether 
osmosis  is  caused  by  electricity  or  whether  a  current  of  electricity 
is  caused  by  osmosis  has  no  bearing  on  flotation.  However,  in 
passing,  it  may  be  of  interest  to  mention  that  Dr.  Robert  Lupke, 
in  his  book,  'Elements  of  Electro-Chemistry'  devotes  Part  III  to 
*  The  Osmotic  Theory  of  the  Current  of-  Galvanic  Cells. ' 

As  mentioned  above,  extreme  dilution  of  the  electrolyte  affects 
the  osmotic  pressure  and  selective  flotation.  With  complete  dissocia- 
tion, as  Arrhenius  has  shown,  the  ionized  molecules  are  free  to 
obey  electric  forces.  It  may  be  freely  granted  that  air  driven  from 
a  particle  by  osmosis  may  effect  a  change  in  the  'contact-film' 
mentioned  by  Mr.  Callow  and  leave  the  particle  negatively  charged, 
so  that  it  would  sink  as  described  by  him.  Also  it  is  granted  that 


™jour.  Phys.  Chem.,  1906,  10,  page  208. 

24'A  Note  on  Taube's  Theory  of  Osmosis  and  Attraction  Pressure,'  by 
F.  H.  Garrison,  Army  Medical  Museum,  Science,  vol.  32,  1910,  page  283. 


FLOTATION   PRINCIPLES  333 

the  mineral  particles  are  all  either  negatively  or  positively  ( ? ) 
charged.  Assuming  the  electric  charges,  there  then  enters  the 
important  question  mentioned  by  Mr.  Callow  in  stating  his  theory 
that  "the  particles  possessing  them  will  migrate  when  placed  in  an 
electric  field."  JThere  is  no  question  but  that  with  an  electric  field, 
flotation  can  be  produced  in  such  a  manner  as  described  by  Bothe 
Schwerin  in  his  'Electro-Osmotic  Process'25  as  follows:  "My  inven- 
tion consists  of  adding  electrolytes  to  the  liquids  containing  the 
substances  to  be  separated,  the  nature  of  the  electrolyte  depending 
upon  the  character  of  the  substance.  If  the  latter  is  of  such  a 
character  that  they  would  be  deposited  by  the  electric  current  on 
the  cathode,  electrolyte  of  acid  character  are  employed;  and  if  the. 
substances  would  be  deposited  on  the  anode,  electrolytes  of  basic 
character  are  used."  Speaking  of  finely-divided  substances,  some- 
times indifferent  to  the  action  of  an  electric  current,  he  continues: 
"I  have  found  that  such  substances  can  be  made  electrically  active 
by  causing  them  to  absorb  [here  used  as  defined  by  Mr.  Ealston] 
colloidal  substances  of  a  strong  electro-positive  or  electro-negative 
character. ' '  Of  the  recent  electrical  theories  advanced,  none  explains 
how  this  important  electrical  field,  mentioned  as  necessary  by  Mr. 
Callow,  is  created  by  any  flotation  machine.  Mr.  Block26  shows  this 
on  a  clay  machine. 

After  selective  flotation  is  created  by  osmosis,  it  matters  not 
whether  the  particles  be  spoken  of  as  being  held  together  or  to 
the  bubbles  by  electric  charges  or  by  cohesion  and  adhesion  in  the 
way  I  mentioned.  Sir  Oliver  Lodge,27  after  saying  that  "the  force 
of  chemical  affinity  has  long  been  known  to  be  electrical"  goes  on 
to  say  that  "there  is  another  kind  of  adhesion  or  cohesion  of 
molecules,  not  chemical,  but  what  is  called  molecular.  This  occurs 
between  atoms  not  possessing  ionic  or  extra  charges,  but  each  quite 
neutral,  consisting  of  paired-off  groups  of  electrons. ' '  However  great 
this  attraction  may  be,  the  mineral  particles  will  not  adhere  to 
bubbles  already  formed,  as  was  shown  above;  but,  using  them  as 
nuclei,  the  nascent  gas  will  form  into  bubbles  to  float  them.  Such 
gas  formation  is  excellently  described  by  Duhem28  as  follows :  ' '  From 
this,  a  bubble  of  vapor  will  never  be  formed  in  a  region  where  the 


25U.  S.  Patent  No.  993,888. 

26'Notes  on  Flotation.'  Discussion.  Bulletin  A.  I.  M.  E.,  Dec.,  1915, 
page  2337. 

27Chapter  16,  'Nature  of  Cohesion,'  in  book  'Electrons,'  by  Sir  Oliver 
Lodge,  Principal  of  the  University  of  Birmingham. 

28'Thermodynamics  and  Chemistry,'  by  P.  Duhem,  1903,  Art.  275,  page  366. 


334  THE  FLOTATION  PROCESS 

liquid  is  continuous;  in  fact,  if  such  a  bubble  could  begin  to  form, 
its  radius  would  be  at  first  infinitely  small — less  than  the  limiting 
radius  of  which  we  have  spoken;  whence,  instead  of  continuing  to 
grow,  it  would  collapse."  On  the  next  page  be  continues:  "These 
considerations  do  not  apply  merely  to  boiling; , they  completely 
explain  a  great  number  of  phenomena/' 

The  electrically-charged  mineral  particles  may  aid  in  bubble 
formation  although  they  cannot  effect  attachment  of  mineral  particles 
to  bubbles  already  formed.  Regarding  this,  Dr.  Thompson29  says 
that  ''the  charged  particles  act  as  nuclei  around  which  small  drops 
of  water  condense,  when  the  particles  are  surrounded  by  damp  air 
cooled  below  the  saturation  point."  "Experiments  were  made  with 
air,  hydrogen,  and  carbonic  acid  and  it  was  found  that  the  ions 
had  the  same  charge  in  all  the  gases."  Also,  "Thus  by  suitably 
choosing  the  super-saturation,  we  can  get  the  cloud  deposited  on 
the  negative  ions  alone  so  that  each  drop  in  the  cloud  is  negatively 
charged."  Electricity  may  manifest  itself  in  various  ways,  but 
flotation  cannot  take  place  without  nascent  or  occluded  gas. 


2»T  he  Atomic  Structure  of  Electricity,'  Chapter  4,  'Electricity  and  Matter.' 
By  J.  J.  Thompson.    Lectures  at  Yale,  May,  1903. 


THE  ELECTRO-STATICS  OF  FLOTATION  335 

THE  ELECTRO-STATICS  OF  FLOTATION 

By  F.  A.  FAHRENWALD 
(From  the  Mining  and  Scientific  Press  of  March  11,  1916) 

The  development  of  every  new  metallurgical  method  is  accom- 
panied by  a  host  of  contradictory  statements  and  widely  differing 
opinions,  but  it  is  only  by  the  elimination  and  correlation  of  parts  of 
recorded  observations  that  a  particular  process  approaches  a  state 
of  perfection.  The  theory  of  notation  has  called  forth  a  number  of 
articles,  each  writer  applying  a  different  hypothesis  in  explaining  the 
puzzling  phenomena  accompanying  the  process. 

Of  the  various  hypotheses  thus  far  advanced  only  two  are  based  on 
principles  of  sufficiently  apparent  soundness  to  warrant  serious  con- 
sideration. 

The  first  of  these  involves  the  physical  surface  phenomena  that 
may  produce  an  inter-facial  tension.  This  has,  until  recently,  been 
accredited  with  more  importance  than  all  the  other  explanations 
combined.  The  second  is  called  the  electrical  theory. 

The  part  that  surface  phenomena  may  play  in  linking  the  particles 
of  ore  to  the  bubble-carriers  is  ably  outlined  by  0.  C.  Ealston,  whose 
treatment1  of  this  phase  of  the  question  includes  reference  to  about  all 
of  the  theory  that  has  so  far  been  found  applicable  to  flotation. 
Without  doubt  a  proper  application  of  the  laws  of  physical  chemistry 
will  disclose  fundamental  principles  upon  which  this  process  may  be 
based;  and  it  may  be  in  the  field  of  colloidal  chemistry  that  most  in- 
formation is  to  be  gained. 

With  regard  to  the  electrical  theory,  however,  there  has  been 
applied  a  number  of  laws  of  electro-statics  that,  from  the  general 
nature  of  conditions  under  which  flotation  is  carried  out,  would  seem 
to  be  inoperative. 

This  hypothesis  has  been  tolerated  by  Mr.  Ealston,2  it  is  strongly 
advocated  by  J.  M.  Callow3,  while  Thos.  M.  Bains,  Jr.,4  excludes  all 
other  theories.  These  three  references  contain  the  gist  of  all  argu- 
ments advanced  in  support  of  this  hypothesis,  and  the  last  of  them 


i'Why  do  Minerals  Float?'  M.  &  8.  P.,  October  23,  1915.  See  also  page  175 
of  this  book. 

20p.  cit. 

3'Notes  on  Flotation.'    M.  &  8.  P.    See  also  page  231  of  this  book. 

4'The  Electrical  Theory  of  Flotation.'  M.  &  S.  P.,  November  27,  1915,  and 
December  11,  1915.  See  also  pages  225  and  258  of  this  book. 


336  THE  FLOTATION  PROCESS 

elaborates  and  definitely  formulates  the  necessary  requirements  for 
flotation  by  electrical  means.  It  is  my  object  to  attempt  an  analysis  of 
the  various  arguments  advanced  in  support  of  the  electrical  theory, 
and  as  the  only  difference  between  this  and  any  other  theory  lies  in  the 
phenomena  that  cause  the  bond  between  the  flotative  mineral  and  the 
bubble-carrier,  it  is  understood  that  only  this  phase  of  the  process  is 
under  discussion.  It  is  necessary,  however,  in  order  to  arrive  at 
practical  conclusions,  that  this  question  be  considered  under  condi- 
tio'ns  similar  to  those  encountered  in  practice. 

Before  proceeding  to  a  discussion  of  the  electrical  theory  of 
flotation  it  will  be  necessary  to  point  out  briefly  a  few  of  the  facts  of 
electro-statics  upon  which  it  is  based. 

A.  The  production  of  electricity  by  friction  is  a  common  phenom- 
enon; almost  any  two  bodies  become  electrified  if  they  are  rubbed 
together.    In  the  case  of  several  substances,  considerable  force  is  then 
necessary  in  order  to  separate  them.     Attraction  or  repulsion  also 
occurs  when  an  electrified  body  is  brought  near  bodies  that  have  been 
subjected  to  friction  and  if  these  are  light  enough  (as  bits  of  pitch, 
feathers,  wood,  paper,  etc. )  they  may  be  lifted.  Bodies  may  also  become 
electrified  by  coming  in  contact  with  other  bodies  that  already  carry  a 
charge.     In  this  case  the  first  body  receives  electricity  of  the  same 
sign  from  the  charged  body  and  is  then  repelled. 

B.  Bodies  that  when  electrified  at  one   point   are  immediately 
electrified  all  over  are  called  good  conductors;  those  over  which  the 
charge  diffuses  slowly  are  poor  conductors.    All  metals,  many  metallic 
ores,  graphite,  ordinary  undistilled  water,  and  aqueous  solutions  of 
salts  are  good  conductors. 

C.  If  a  piece  of  metal,  or  other  conducting  material  held  in  the 
hand  is  rubbed  against  a  non-conductor — say,  a  piece  of  dry  flannel — 
only  the  non-conductor  appears  afterward  to  be   electrified.     The 
reason  is  that  the  electrification  produced  on  the  metal  spreads  over 
the  hand,  arm,  and  body  of  the  experimenter  to  the  floor  and  walls  of 
the  room.    If,  however,  the  conductor  be  insulated,  the  degree  of  its 
electrification  cannot  be  increased  or  decreased. 

D.  By  whatever  process  a  body  is  electrified  there  is  always  an 
equal  amount  of  electricity  of  the  opposite  sign,  which  may  reside 
upon  the  walls  of  the  enclosing  room  or  upon  some  other  surface  in- 
sulated from  the  conductor.    Bodies  carrying  opposite  charges,  when 
brought  in  contact  or  connected  by  a  conductor,  become  discharged. 
If  the  charges  are  equal  they  are  neutralized,  but  if  one  carries  more 
than  the  other  the  system  takes  on  the  sign  of  the  excess  charge. 


THE   ELECTRO-STATICS   OF   FLOTATION  337 

E.  If  these  bodies  are  strongly  electrified,  discharge  can  take  place 
through  an  appreciable  thickness  of  non-conducting  material,  such  as 
air,  oil,  or  glass.    This  discharge  is  facilitated  by  the  presence  of  sharp 
projections  upon  either  body. 

F.  (a)    The  space  between  two  charged  bodies  is  filled  with  lines 
of  force  that  tend  to  move  a  contained  body  in  the  direction  of  the 
local  lines  of  force  leading  to  the  surface  carrying  the  opposite  sign. 

(b)  These  lines  of  force  do  not  penetrate  the  surface  of  the  con- 
ductors forming  its  boundaries  and  a  hollow  conductor  is  electrified 
on  its  outside  or  inside  surface  only,  depending  upon  whether  the 
opposite  charge  resides  upon  one  contained  without  the  sphere  or 
upon  one  contained  within  and  insulated  from  the  shell.  In  the 
latter  case  the  entire  field  is  contained  within  the  inner  surface  of 
the  sphere,  and  in  the  former  case  there  is  no  charge  within  the  hollow 
conductor. 

G.  The  force  exerted  between  two  small  charged  bodies  is  given  in 

qq1 

the  equation  F  =  -^-  in  which  q  and  q1  are  the  charges  in  electro- 
static units  carried  by  each  of  the  two  bodies,  and  d  is  the  distance 
between  their  centres  of  charge.5  If  the  bodies  are  separated  by  a 
medium  other  than  air  a  factor  K,  known  as  its  dielectric  coefficient, 

1      qq1 

must  be  used,  and  the  equation  becomes  F  =  r-  •  —rj- 

K          Cl 

H,  Matter  itself  is  not  acted  upon  by  an  electric  force,  which  acts 
only  between  different  quantities  of  electricity.  When  a  conductor 
is  introduced  into  an  electric  field  it  represents  a  gap  or  an  interrup- 
tion of  the  lines  of  force,  resulting  in  an  electrification  of  its  surfaces 
only,  that  part  becoming  positive  which  is  presented  toward  the  nega- 
tive boundary  of  the  field  and  the  reverse.  In  other  words,  the  original 
field  is  divided  into  two.  This  same  effect  is  produced  in  the  case  of 
a  poor  conductor  but  to  an  exceedingly  small  degree.  This  explains 
the  attraction  of  small  bodies  by  another  that  has  been  electrified  by 
friction,  in  which  case  electrification  by  influence  precedes  attraction, 
and  what  is  really  observed  is  attraction  between  opposite  electric 
charges. 

Before  considering  these  fundamental  laws  of  electro-statics  in 
connection  with  an  explanation  of  flotation  phenomena,  it  may  be 
well  to  consider  briefly  the  conditions  under  which  different  phases 
of  this  process  take  place. 


sThe  force  exerted  by  a  charged  sphere  acts  as  if  originated  at  the  centre. 


338  THE  FLOTATION  PROCESS 

Of  first  importance  is  the  fact  that  all  operations  are  carried  out 
in  conducting  solutions  which  in  every  case  are  earthed.  It  is  incon- 
ceivable that,  after  any  grinding  process  has  been  applied  in  machines 
such  as  are  commonly  used,  the  individual  positively  charged  particles 
of  ore  should  not  have  come  in  contact  with  negatively  charged  bodies 
and  with  conducting  parts  of  grinding  and  mixing  machinery,  even 
if  oil  has  been  added  in  a  preliminary  stage.  The  ore  particles  are 
conductors,  the  oil  is  a  non-conductor,  the  bubbles  are  filled  with  non- 
conducting air,  and  the  gangue  is  composed  of  non-conducting 
material. 

These  conditions  being  granted,  the  next  step  will  be  to  apply  the 
laws  of  electro-statics  to  criteria  for  flotative  conditions  according  to 
the  electrical  theory,  as  summarized  by  Mr.  Bains.  These  include 
the  main  ideas  of  Mr.  Callow's  article  and  of  the  theory  in  general, 
so  that  a  discussion  of  these  in  order  will  apply  to  the  various  other 
articles  advancing  a  similar  hypothesis. 

1.  "Ores  containing  valuable  minerals  or  metals  that  are  good 
conductors  are  the  only  ones  that  are  suitable  for  flotation. " 

This  seems  in  general  to  be  true,  but  the  ratio  of  flotative  tendency 
to  conductivity  of  the  different  ore  constituents  is  nothing  like  a 
constant.  For  instance,  the  conductivity  of  galena  is  to  the  conductiv- 
ity of  chalcocite  as  35 : 1.  Their  flotative  tendencies  hardly  bear  this 
ratio. 

In  entire  opposition  to  this  supposed  requirement  I  found  that 
small  pieces  of  diamond  attract  a  grease6  or  oil  coating  and  attach  to 
bubbles  quite  as  readily  as  does  galena. 

2.  "To  buoy  these  conductors,  it  is  necessary  to  supply  enough 
electrified  bubbles  from  below  to  float  particles  of  the  conductors  that 
are  attracted;  hence  the  smaller  the  bubble,  the  better  the  result, 
the  amount  of  gas  being  the  same. ' ' 

A  bubble  within  a  solution  of  various  salts  and  acids  presents  a 
similar  condition  to  that  of  the  air-space  within  a  hollow  conducting 
sphere.  It  is  known  (see  F  (b)  above)  in  this  case  that  in  order  to 
have  a  charge  upon  this  inner  surface  it  is  necessary  that  an  opposite 
charge  be  maintained  within  and  insulated  from  it.  In  the  case  of 
the  bubble  there  is  nothing  inside  to  carry  the  charge.  In  case  this 
space  carried  water-vapor  or  ionized  gases,  a  charge  could  be  present, 
but  it  would  be  dissipated  quickly  by  diffusion  of  these  charged  par- 
ticles and  resulting  contact  with  the  water-surface. 

If  this  sphere  did  contain  charged  gases  and  was  lined  with  oil, 


eThis  fact  is  utilized  in  the  recovery  of  diamonds  at  Kimberley. 


THE   ELECTRO-STATICS   OF   FLOTATION  339 

there  would  be  present  the  condition  of  the  hollow  conducting  spheres, 
(F  (b) )  with  enclosed  charged  conductor  insulated  from  it,  and  carry- 
ing an  opposite  charge.  The  charges  would  be  equal  and  the  amount 
governed  by  the  charge  on  the  inside  sphere.  These  charges  being 
balanced,  the  bubble  system  could  have  no  influence  upon  a  body- 
charged  or  not — without  the  outer  sphere,  such  as  a  particle  of  galena 
suspended  in  the  water  at  a  distance.  There  can  be  no  attraction 
through  the  intervening  conductor,  as  lines  of  force  will  not  penetrate 
a  conducting  surface. 

It  appears  evident  then  that,  first,  unless  a  bubble  contains  charged 
bodies  (ionized  gas,  water-vapor,  or  solid)  within  its  bounding  sphere 
it  can  carry  no  charge ;  second,  that  unless  it  is  lined  with  a  dielectric 
the  charge  will  be  rapidly  dissipated;  and,  third,  even  though  a 
charge  is  present  and  insulated  from  the  outer  conducting  sphere  it 
can  have  no  attraction  for  any  body  or  charge  without  the  outer 
sphere,  through  a  thickness  of  solution. 

3.  "Some  dielectric  fluid  is  necessary  to  cover  the  conductor  or  the 
bubble,  to  prevent  the  dissipation  of  the  electric  charge.  The  thinner 
the  film  of  dielectric  and  the  greater  its  dielectric  strength  the 
greater  the  attractive  force  and  the  more  permanent  will  be  the  froth." 

The  bubble,  both  insulated  and  otherwise,  has  been  considered. 
The  particle  of  ore,  unless  insulated,  will  be  immediately  discharged 
by  coming  in  contact  with  a  grounded  conductor — the  solution.  It  is 
immaterial  whether  the  opposite  charge  is  carried  by  the  water  or  by 
some  other  surface,  the  effect  will  be  the  same.  Assume,  however, 
that  the  ore  particle  is  charged,  and  insulated.  Again  we  have  the 
case  of  one  charged  conductor  (the  ore)  being  enclosed  within 
another  (the  surrounding  water  solution)  giving  a  system  which 
is  neutral  with  regard  to  any  other  charge  or  system  without  the 
outer  sphere. 

Under  conditions  electro-statically  ideal  these  forces  may  be 
pictured  as  in  Fig.  79.*  Both  bodies  are  charged  and  insulated,  and 
suspended  in  an  intervening  conducting  medium.  The  systems  ore- 
oil-water,  and  gas-oil-water,  are  without  effect  upon  each  other. 

In  case  the  gas  is  generated  from  the  ore  the  particle  could  not 
be  insulated  unless  by  some  phenomenon  not  understood  at  present. 
If  the  gas  is  air  passed  mechanically  into  the  pulp  it  would  be  forced 
into  contact  with  ore  particles,  in  which  case  the  charges  carried  by 
each  would  have  its  effect  upon  the  other.  That  a  mass  of  air  con- 


*See  page  342. 


340  THE  FLOTATION  PROCESS 

taining  charged  vapor  or  gases  could  be  insulated  before  coming  in 
contact  with  the  conducting  solution  is  not  reasonable. 

Assuming,  however,  that  both  bodies  are  charged,  so  that  the 
second  part  of  No.  3  (above)  regarding  the  thickness  of  insula- 
tion may  now  be  considered.  It  has  been  proved  that  the  force 
exerted  by  a  charged  sphere  acts  as  if  it  was  concentrated  at  the 
centre.  Bearing  this  in  mind  it  is  evident  that  in  the  case  of  particles 
of  the  size  with  which  flotation  deals,  a  separation  of  their  surfaces 
by  one  micron  or  one  millimetre  will  produce  little  practical  difference 
in  the  force  exerted  between  them. 

4.  "Some  material  must  be  added  to  the  water  to  increase  its 
conductivity,  to  obtain  a  clean  concentrate:  acids  in  small  amounts 
are  now  used.  '  ' 

This  factor  has  been  considered  under  divisions  2  and  3.  The 
working  solution  is  a  conductor,  parts  of  which  are  interposed  between 
the  various  charged  particles,  thereby  breaking  all  lines  of  force 
between  them. 

In  any  attempt  to  determine  experimentally  whether  or  not 
electro-static  forces  play  any  considerable  part  in  holding  the  bubble 
and  particles  of  ore  together  it  is  rather  difficult  to  select  tests  which 
will  give  results  of  value.  If  these  forces  act  to  the  exclusion  of  all 
others  it  is  evident  that  they  would  be  represented  by  charges  of  easily 
measurable  magnitude.  For  example,  I  have  separated  particles  of 
galena,  (uncoated  with  oil)  that  have  been  carried  to  the  top  of  an 
acid  solution,  weighing  60  mg.  (52  mg.  in  water).  To  hold  a  particle 
of  this  size  to  the  surface  of  a  bubble  requires  50.9  dynes  —  call  it  50 
in  round  numbers.  The  diameter  of  this  particle  is  about  2  milli' 
metres.  The  bubble  required  to  buoy  this  particle  must  displace  at 
least  52  mg.  water  or  in  other  words  its  volume  must  be  52  mm3.  Its 
diameter  would  be  about  5.2  mm.  Using  these  figures  the  equation 

QQ1 
for  force  becomes  52  (dynes)  =  -        or  assuming  the  charges  to  be 


balanced 

Q2  =  673.92 

Q   =25.9  c.  g.  s.  electro-static  units. 

It  is  not  likely  that  a  particle  of  ore  or  a  bubble  of  the  nature  given 
can  have  a  charge  of  this  magnitude,  for  the  reason  that  a  potential 
of  this  intensity  would  discharge  through  a  very  strong  dielectric. 
Experiments  have  been  carried  out  that  give  ratios  for  electro-static 
units,  potentials,  and  distance  through  which  discharge  will  take  place 
in  air,  using  brass  knobs  of  one  centimetre  diameter. 


THE   ELECTRO-STATICS   OF   FLOTATION  341 

Volts  at  dis-  Distance 

Electro-static  units.        charge  potential.  between  knobs. 
16.1                                 4830  0.1  cm. 

56.3  16890  0.5     " 

84.7  25404  1.0     " 

According  to  these  figures  the  charge  necessary  to  exert  a  force  of  50 
dynes  in  lifting  a  particle  of  galena  would  be  so  intense  that  it  would 
discharge  through  a  dielectric  as  strong  as  air  at  the  distance  by 
which  the  centres  of  charges  are  separated.  Not  satisfied,  however, 
with  this  apparent  theoretical  disproval  of  the  electric  theory  I 
undertook  a  series  of  experiments7  that  should  serve  to  check  the 
various  points  in  the  above  theoretical  discussion. 

No.  1.  Galena  ore  was  ground  in  an  agate  mortar  and  poured  from 
an  agate  spoon  (to  prevent  discharge  of  positive  electricity,  if  present, 
from  ore)  between  two  plates  of  an  electro-static  machine.  The  ma- 
terial was  deflected  as  shown.  Plates  were  electrified  almost  to  dis- 
charge point.  This  shows  that  galena  ground  under  insulating  con- 
ditions carries  a  charge  and  that  a  particle  of  this  nature,  suspended 
in  a  non-conductor  in  an  electro-static  field,  is  attracted. 

No.  2.  Ore  was  ground  in  conducting  earthed  mortar  and  poured 
from  earthed  spoon.  Deflection  of  only  a  very  few  particles  was 
shown.  Perhaps  the  deflected  particles  were  insulated  with  oil  or  did 
not  come  in  contact  with  earthed  surface. 

No.  3.  Ore  treated  as  in  No.  1  and  poured  between  glass  sides  of 
a  cell.  Glass  was  1  mm.  thick  and  separated  by  2  cm.  Potential  be- 
tween plates  of  machine  was  8500  volts.  Deflection  as  shown.  The 
interposition  of  glass  had  very  little  effect. 

No.  4.  As  in  No.  3,  but  the  cell  was  full  of  water.  Used  conduc- 
tivity, tap,  and  acid  water.  No  deflection.  This  indicates  that  par- 
ticles charged,  or  otherwise,  suspended  in  a  conducting  solution  (i.  e., 
enclosed  within  our  hypothetical  conducting  sphere)  is  not  affected  by 
electro-static  forces  without. 

No.  5.  Cell  contained  ore  and  nitric  acid  solution  to  generate  gas. 
Neither  bubble  rising  or  ore  particles  dropping  showed  deflection. 
Potential,  10,000  volts.  The  conditions  here  duplicate  those  of  No.  4. 

No.  6.  Bubbles  blown  through  canvas  into  water  or  acid  solu- 
tion were  not  deflected.  A  charge  of  bubbles  flowing  in  one  direction 


7The  writer  is  greatly  indebted  to  the  departments  of  Metallurgical  En- 
gineering and  of  Physics  in  the  Case  School  of  Applied  Science  for  laboratory 
facilities  and  apparatus  placed  at  his  disposal  in  carrying  out  these  ex- 
periments. 


342 


THE   FLOTATION    PROCESS 


would  produce  an  electric  current,  and  even  if  they  were  charged  they 
could  not  be  attracted,  as  here  again  the  charges  are  enclosed  in  a 
conducting  material. 


si 

ir 


F/G.1 


— 0 


F/6.Z 


Fl&.S 


0 


FIG-.5 


V 4r-/\IR 


Jj$i 


FI6.J 


FIG.  78. 


FIG.    79. 


No.  7.  Ore  poured  into  cell  containing  gasoline.  There  seemed 
to  be  a  slight  deflection.  10,000  volts  between  plates.  Conditions  here 
should  not  differ  greatly  from  those  of  No.  3.  Solution  may  not  have 
been  sufficiently  non-conducting. 


THE  ELECTRO-STATICS   OF   FLOTATION  343 

No.  8.  Solution  placed  in  electrolytic  cell,  arranged  as  shown,  gave 
no  deflection  of  ore  or  bubble  with  conducting  or  non-conducting  so- 
lution. Both  ions  and  charged  colloids  are  susceptible  to  this  treat- 
ment, and  no  doubt  they  would  move  easier  than  the  larger  body  and 
so  lessen  the  potential  on  the  larger  masses. 

No.  9.  The  water  itself  was  electrolyzed  to  furnish  gas.  A  two- 
way  switch  gave  either  hydrogen  or  oxygen  at  the  bottom  pole,  which 
was  covered  with  a  layer  of  ore.  Both  gases  carried  apparently  equal 
amounts  of  ore  and  with  equal  readiness.  Bubbles  in  either  case,  upon 
striking  the  "upper  plate,  did  not  discharge  their  burden  of  ore,  no 
matter  what  the  sign  of  electrode. 

No.  10.  Set  up  as  in  No.  9,  except  that  gas  was  furnished  by  action 
of  nitric  acid  on  ore.  Changing  of  sign  produced  no  discernible  effect 
upon  bubble  or  ore  or  upon  bubbles  with  load  when  coming  in  contact 
with  upper  electrode  plate. 

I  wish  to  point  out  the  fact  that  this  discussion  and  these  results 
are  to  be  considered  only  in  connection  with  the  bond  between  a  bubble 
and  ore  particles.  The  conditions  chosen  have  been  ideal,  in  order 
to  isolate  this  particular  phase  of  the  problem.  Particles  of  appreci- 
able mass  (+200-mesh)  have  been  used,  but  this  permits  of  an 
electro-static  consideration  without  interference  from  exaggerated 
surface  conditions  due  to  smaller  bodies.  It  is  possible  that  an  ionized 
solution  does  not  behave  like  a  solid  metallic  conductor  toward  an 
electro-static  charge,  but  I  know  of  no  evidence  to  the  contrary.  Very 
little  is  known  regarding  contacts  between  solid-liquid-gas  phases,  but 
it  is  doubtful  whether  charges  such  as  accompany  phases  of  a  colloidal 
solution  are  of  much  influence  in  the  case  of  bodies  of  the  size  herein 
considered.  It  may  be  found  that  the  oil-water  emulsion  or  the  oil- 
films  introduce  the  colloidal  element,  and  no  doubt  many  of  the  slimes 
contain  colloids,  in  which  the  electric  charges  are  of  great  importance. 
It  is  known  that  masses  of  sulphides,  such  as  galena,  are  positive,  but 


Assume  edge  o 
cube  to  be 
1            cm 

f 
Number  of  cubes. 
1 

Surface. 
6  cm 

01 

103 

60  " 

0.01        "  . 

106 

600  " 

0  001 

109 

6  000  " 

0.0001     " 

(one  micron  (u)).                    1012 

6  sq   m 

0.0005     " 

(size  of  particles  in  kaolin  suspension) 

0.00001  =  micron  1013  60 

0.01  micron  (limit  of  ultra-microscopy) .  1014  600 

0.001        "      —  one  millimicro   (mu) . . .  1021  6,000 

0.1     mu.  =  hydrogen  molecule..             .  1024  60,000 


344  THE  FLOTATION  PROCESS 

these  same  sulphides  in  colloidal  form  are  negative.  Metals  in  mass 
and  as  atoms  are  positive  but  these  also  as  colloids  are  negative. 
This  complicates  considerably  the  electrical  theory  in  the  case  of  pulp 
containing  both  sand  and  slime.  It  may  be  interesting  to  call  attention 
to  the  enormous  increase  of  surface  produced  by  subdivision,  in  which 
case  phenomena  that  are  purely  superficial  are  greatly  enhanced. 

When  it  is  considered  that  these  small  particles  contain  the  energy 
necessary  to  subdivide  them,  whether  electrical  or  otherwise,  it  is 
apparent  that  phenomena  encountered  throughout  a  range  in  size  of 
particle  body  will  not  bear  a  direct  ratio  to  its  mass  or  constituent 
material.  A  consideration  of  this  phase  of  the  subject  is,  however, 
without  the  scope  of  this  paper,  which  is  only  given  to  point  out  a  few 
of  what  would  appear  to  be  misapplications  of  the  laws  of  electro- 
statics. 


ON   THE   SCIENCE   OF   A   FROTH 

By  WILL  H.  COGHILL 
(From  the  Mining  and  Scientific  Press  of  February  26,  1916) 

The  paragraph  on  the  character  of  froth  in  Mr.  Callow's  article 
in  the  Mining  and  Scientific  Press  of  December  4,  1915,  page  852,  led 
me  to  refer  to  some  notes  that  have  been  pigeon-holed  for  some  months. 
I  think  that  a  little  mathematics  can  be  applied  to  good  advantage. 

Before  taking  up  the  mathematics,  however,  I  wish  to  mention 
some  principles  that  I  think  have  not  been  sufficiently  emphasized  in 
the  articles  on  flotation ;  that  is,  a  distinction  between  the  properties 
of  aqueous  and  non-aqueous  films. 

The  little  book  on  'Surface  Tension  and  Surface  Energy7  by 
Willows  &  Hatschek  shows  how  the  elastic  film  analogy  in  the  study 
of  froth  will  get  one  into  no  end  of  trouble  if  not  handled  with  care. 
It  is  the  characteristic  of  analogies  to  break  down  when  pressed  too 
far,  though  they  are  useful  up  to  a  certain  point.  This  one  is  no  ex- 
ception. In  the  case  of  india-rubber  it  is  obvious  that  a  given  weight 
can  only  stretch  this  to  a  definite  extent.  To  further  enlarge  the 
rubber  film,  an  additional  weight  would  be  required;  while  with  a 
liquid  film  this  is  not  true.  Reference  to  a  recent  article1  shows  that 
the  measure  of  surface  tension  is  not  when  the  film  breaks  but  at  the 
instant  when  the  wire  is  pulled  away  from  AB.  If  the  wire  is  pulled 

iT.  A.  Rickard,  M.  d  8.  P.,  Sept.  11,  1915.    See  page  127. 


ON  THE  SCIENCE  OF  A  FROTH  345 

a  great  distance  without  breaking  the  film,  the  total  energy  of  the 
surface  is  increased,  of  course,  but  the  energy  per  unit-area  and 
surface  tension  are  unaffected.  Whether  or  not  the  film  breaks, 
depends  not  upon  the  surface  tension,  but  whether  or  not  there  is 
enough  liquid  to  supply  the  added  area.  The  difference  between  a 
non-aqueous  substance  and  a  liquid  film  is,  that  in  stretching  the 
former  the  molecules  are  distorted  or  separated  while  in  stretching  a 
liquid  film  molecules  come  from  within  the  liquid  to  occupy  the  new 
area.  According  to  Devaux2  the  surface  tension  phenomenon  dis- 
appears as  soon  as  there  is  no  more  liquid  to  come  from  within.  The 
same  laws  apply  to  surfaces  that  are  allowed  to  contract.  The  rubber 
has  a  constantly  decreasing  force  of  contraction  as  it  approaches  its 
original  dimensions,  while  a  liquid  film  always  tends  to  contract  with 
the  same  force  independently  of  its  size.  Now,  it  is  a  common  practice 
in  demonstrating  physical  principles  to  omit  certain  qualifying  con- 
ditions until  the  main  features  are  outlined.  This  method  must  be 
pursued  here.  The  qualifying  statement  is,  that,  in  the  case  of  a 
contaminated  liquid  the  film  may  not ' '  contract  with  a  force  independ- 
ently of  its  size ; ' '  that  is,  after  learning  to  look  upon  surface  tension 
as  a  constant  force  we  must  now  view  it  as  a  variable  force.  Take, 
for  example,  the  explanation  of  the  effect  of  oil  on  waves.3  When 
a  small  wave  is  formed  on  the  surface  of  water  the  surface  is  stretched ; 
for  obviously  the  wavy  surface  has  greater  area  than  the  plane  sur- 
face. Owing  to  the  stretching  of  the  surface  the  oil  film  is  made 
thinner  so  that  the  contamination  due  to  oil  is  reduced,  and  hence  the 
surface  tension  is  increased;  this  increase  in  surface  tension  tending 
to  oppose  the  production  of  the  wave. 

Again,  Edser4  discusses  variable  surface  tension  under  the  head- 
ing 'Stability  of  a  Liquid  Film/  He  shows  that  when  a  film  is  on  a 
vertical  rectangle5  equilibrium  is  impossible  unless  the  surface  tension 
is  greater  at  the  top  than  at  the  bottom  of  the  film.  This  is  obviously 
due  to  the  weight  of  the  film  itself.  For  pure  water,  the  surface 
tension  is  nearly  constant,  and  therefore,  a  water  film  more  than  two  or 
three  millimetres  in  height  cannot  be  formed.  A  slight  trace  of  grease 
will  give  the  water  a  variable  surface  tension ;  if  the  surface  tension  at 
any  point  on  the  film  is  insufficient  to  produce  equilibrium,  the  film 


Films  on  Water  and  on  Mercury.'    M.  &  S.  P.,  July  31,  1915. 
3J.  W.  Watson,  'General  Physics,'  page  113. 
*Edwin  Edser,  'General  Physics  for  Students,'  page  348. 
sThe  cut  of  the  rectangle  was  shown  in  the  article  previously  referred  to 
in  the  M.  &  S.  P.,  Sept.  11,  1915. 


346  THE  FLOTATION  PROCESS 

stretches  at  this  point,  and  the  concentration  of  grease  is  diminished, 
so  that  the  surface  tension  increases  automatically  and  equilibrium  is 
maintained. 

He  concludes  by  saying  that  the  great  stability  of  a  soap  film  is 
due  to  the  wide  variation  in  surface  tension  between  freshly  formed 
and  long  exposed  parts  of  the  surface  and  that  any  stretching  of  the 
film,  due  to  insufficient  strength,  immediately  increases  the  surface 
tension.  Now  it  seems  to  me  that  it  is  time  for  us  to  get  away  from  the 
idea  that  low  surface  tension  per  se,  is  necessary  for  the  formation 
of  a  froth,  for  Edser  has  made  it  clear  that  the  contamination  of  the 
film  with  something  that  will  give  a  variable  surface  tension  is  the 
essential.  To  be  sure  this  amounts  to  reducing  surface  tension  because 
contamination  of  water,  with  some  exceptions,  has  this  effect.  The 
attorney  who  discoursed  at  great  length  upon  surface  tension  and 
said  that  the  longevity  of  a  bubble  was  increased  by  decreasing  the 
contractile  drawing  force  of  surface  tension,  was  merely  riding  too 
far  the  willing  horse  that  many  of  us  have  ridden  so  freely. 

It  is  quite  easy  to  accept  the  statement  that  soap  contaminates 
water  enough  to  afford  a  variable  surface  tension,  but  it  is  not  quite 
so  clear  how  a  very  small  fraction  of  1%  of  oil  will  give  the  same 
results,  until  we  have  considered  adsorption. 

Adsorption  has  been  described  several  times  in  the  technical 
journals  but  I  believe  I  am  justified  in  taking  it  up  again  and  quoting 
from  *  Surface  Tension  and  Surface  Energy, '  because  here  we  find  the 
generalized  statement  describing  adsorption  in  a  liquid  and  its  effect 
on  surface  tension.  It  says:  "If  the  dissolved  substance  diminishes 
the  surface  tension  of  the  solution,  an  excess  of  concentration  in  the 
surface  layer  diminishes  surface  energy.  If  on  the  other  hand,  the 
solute  increases  the  surface  tension  the  surface  energy  will  be  reduced 
if  the  concentration  in  the  surface  layer  is  lower  than  that  of  the  bulk 
of  the  solution.  This  difference  in  concentration  between  the  surface 
layer  and  the  bulk  of  the  solution  is  called  adsorption  and  is  a  physical 
fact.  The  factors  tending  to  produce  adsorption  are  opposed  to  the 
factors  tending  to  establish  uniform  concentration.  The  final  dis- 
tribution of  a  solute  is  the  resultant  of  adsorption  and  two  other 
effects,  namely,  osmotic  pressure  and  electric  charge.  Important 
qualitative  conclusions  are  drawn  from  theoretical  considerations 
already  developed.  A  small  quantity  of  dissolved  substance  may  re- 
duce the  surface  tension  very  considerably,  but  it  can  only  increase  it 
slightly.  Thus,  sodium  chloride  increases  surface  tension  of  water 
to  a  small  extent ;  the  concentration  in  the  surface  layer  is  accordingly 


ON  THE  SCIENCE  OF  A  FROTH  347 

smaller  than  in  the  bulk,  and  the  effect  of  the  solute  is  thus  partly 
counteracted.  On  the  other  hand,  many  organic  salts  reduce  surface 
tension,  and  therefore  accumulate  in  the  surface  layer;  so  that  in 
extreme  cases,  the  whole  of  the  solute  may  be  collected  there  and 
produce  a  considerable  effect,  although  the  absolute  quantity  may  be 
exceedingly  slight. ' ' 

Adsorption  is  of  such  unmistakable  importance  that  we  will 
refer  to  'The  Chemistry  of  Colloids'  by  W.  W.  Taylor  for  a  different 
perspective  of  the  same  thing.  Here  I  quote  freely,  for  I  am  not 
intending  to  advance  my  own  theories  but  to  bring  out  what  seem  to  me 
to  be  the  pertinent  physical  facts.  And  here  I  wish  to  state  that  I 
fear  that  the  premise  for  my  recent  calculation6  of  the  carrying 
capacity  of  the  surface  of  a  liquid  is  not  correct.  It  was  an  attempt 
to  elaborate  on  a  weak  statement  in  a  text-book  and  hence  the  calcu- 
lations themselves  cannot  be  credited. 

Adsorption,  in  its  most  general  sense,  implies  the  unequal  dis- 
tribution of  substances  at  the  boundary  between  two  heterogeneous 
phases:  solid-gas,  solid-liquid,  and  liquid-gas.  We  are  concerned 
just  now  with  only  the  last. 

The  surface  layer  of  a  liquid  is  under  great  compression  due  to  the 
great  difference  of  the  molecular  forces  on  the  two  sides  of  the  inter- 
face and  consequently  the  concentration  in  the  surface  of  a  solution 
must  be  different  from  that  in  the  bulk  of  the  liquid.  For  just  as 
unequal  temperatures  in  a  dilute  solution  cause  an  unequal  distribu- 
tion of  the  solute,  so  from  the  same  law  unequal  pressures  must  also 
produce  an  unequal  distribution.  This  pressure  (due  to  surface  ten- 
sion) always,  in  time,  adjusts  itself  to  the  minimum,  for  a  component 
which  lowers  surface  tension  is  always  increased  in  the  surface  layer 
whether  the  component  be  present  as  solvent  or  solute. 

We  now  have  a  new  principle  to  apply  to  a  bubble,  to  wit:  on 
account  of  adsorption  a  fresh  surface  always  has  a  greater  surface 
tension  than  an  old  one;  thus  if  it  is  stretched  locally  by  conditions 
tending  to  break  it,  it  is  automatically  reinforced  at  that  point. 

It  is  now  obvious  that  without  adsorption  it  would  be  impossible 
to  realize  a  variable  surface  tension,  for  if  the  solution  were  contam- 
inated uniformly  throughout,  a  fresh  surface  exposed  by  the  stretch- 
ing of  the  film  would  have  the  same  energy  as  the  old  surface  and  the 
ultimate  result  would  be  identical  with  the  case  cited  where  pure  water 
was  used. 

In  this  argument  I  have  assumed  that  the  contaminating  substance 


ePage  158. 


348  THE  FLOTATION  PROCESS 

is  soluble  in  water.  I  realize  fully  that  many  of  the  flotation  oils  are 
said  to  be  insoluble  in  water,  but  I  maintain  that  solubility  is  only 
relative,  and  further,  we  know  nothing  about  the  multiplicity  of 
chemical  reactions  possible  in  a  pulp  which  might  release  contaminat- 
ing substances  that  would  produce  the  adsorption  phenomenon.  If 
graphite,  for  instance,  acts  as  a  frothing  agent,  it  might  have  to  be 
treated  as  a  special  case  and  could  not  be  taken  as  proof  that  the 
above  arguments  are  invalid.  If  the  flotation  oil  is  extremely  insoluble 
in,  and  lighter  than,  water  there  would  be  an  oil  film  at  the  liquid- 
air  interface  and  over  the  liquid  film  containing  adsorbed  oil.  It 
might  be  well  at  this  point  to  drop  the  subject  of  variable  surface 
tension  and  undertake  to  get  a  better  idea  of  the  absolute  value  of 
these  forces.  One  physicist  has  spoken  of  them  as  being  enormous. 

As  far  as  surface  tension  is  concerned  it  is  theoretically  possible 
to  blow  a  soap  bubble  as  big  as  a  house. 

Take  the  formula : 

a)  p=^ 

Where  T  =  pull  due  to  surface  tension  in  grams  of  a  film  of  one 
surface  and  1  cm.  long. 

P  =  excess  pressure  inside  per  unit-area,  and  r  =  the  radius  of  the 
sphere. 

This  formula  takes  into  account  the  pull  on  both  the  internal 
and  external  surfaces.  It  needs  no  demonstration,  as  it  is  derived  in 
the  same  manner  as  the  old  familiar  formula  used  in  calculating  the 
thickness  of  boiler-shells,  etc. 

In  case  of  a  liquid  drop  or  a  bubble  submerged  in  water,  the 
formula  is: 

(2)     P=^ 

Now  let  us  use  these  formulae  to  make  a  little  study  of  the  mathe- 
matics of  a  bubble  to  see  how  much  a  variation  of  surface  tension  and 
external  pressure  amount  to  when  numerically  expressed  and  see  if 
Mr.  Callow's  argument  is  good. 

He  states:  "The  bubbles  *  *  being  generated  under  a  hydraulic 
pressure  varying  from  15  to  40  inches,  on  rising  above  the  water  *  * 
burst  by  reason  of  the  lower  surrounding  atmospheric  pressure." 
This  pictures  the  emerging  bubble  as  expanding  like  a  bladder  when 
suddenly  inflated  by  increased  internal,  or  decreased  external,  pres- 
sure, and  is  a  misconception.  To  make  the  steps  more  simple  we  will 
first  study  the  bubble  in  air  and  then  when  submerged. 

Assume  1  cc.  of  free  air  taken  in  form  of  a  sphere 


ON  THE  SCIENCE  OF  A  FROTH  349 

(3)  V  =  4.2r3  =  l 
r  —  0.620  cm. 

Now  suppose  this  air  to  be  enclosed  in  a  liquid  film  in  air  where  the 
liquid-air  surface  tension  is  70.  The  new  radius  can  be  calculated 
by  the  application  of  Boyle's  law,  which  is,  that  the  pressure  varies 
inversely  as  the  volume,  where  absolute  pressure  is  of  course  under- 
stood. The  free  air  is,  in  round  numbers,  under  a  pressure  of  1000 
gm.  per  sq.  cm.  and  a  surface  tension  of  70  dynes  per  cm.  exerts  a  pull 
equivalent  to  weight  of  approximately  0.07  gm.  per  cm.  of  length. 

The  proportion  used  to  calculate  the  new  radius  is  : 

1000    :    (1000+^)    ::  4.2r3  :  1 

(4)  4200r3  +  1.176r2  =  1000 
r  =  0.619 

4T        0.28          n  .__ 
:  T*  :"  0^619  =  °'453  gm<  Per  S(*'  Cm' 

The  second  term  of  equation  (4)  is  the  only  one  that  contains  a 
function  of  surface  tension,  and  since  it  is  of  such  small  numerical 
value,  it  is  plain  that  any  variation  of  surface  tension  has  very  little 
to  do  with  the  radius  of  an  individual  bubble  in  air.  Even  when  the 
surface  tension  varies  between  zero  and  a  maximum,  as  in  (3)  and 
(4),  the  change  of  radius  is,  in  fact,  too  slight  to  be  calculated  on  the 
slide-rule  —  only  from  0.620  to  0.619  cm.  It  is  interesting  to  note 
that  P  has  a  value  of  0.453  gm.  per  sq.  cm.  which  equals  0.006  Ib.  per 
sq.  in.  This  is  the  order  of  magnitude  of  the  forces  that  cause  a  spray 
above  the  froth. 

Suppose  again  that  the  bubble  is  1  cm.  below  surface.  We  then 
have: 

(5)  1000   : 
r  =  0.618 


Total  pressure  1  +  0.226  =  1.226  (gauge) 

Finally  take  a  depth  of  75  cm. 

(6)     1000    :   (1075  +  ?iL)   ::  4.2r3  :  1 

r==  0.561 

p  _  2T         0.14 

:= 


Total  pressure  =  75  +  0.250  =±=  75.250   (gauge) 
These  results  are  shown  in  the  appended  table  : 


350  THE   FLOTATION   PROCESS 

ONE  CUBIC  CENTIMETRE  FBEE  AIR 

Gauge  Absolute 

No.                  Description.                       r                   P          pressure.  pressure. 

3  Free   air    0.620            0.000              0.000  1000.000 

4  Liquid  film  in  air 0.619            0.453              0.453  1000.453 

5  Submerged  1  cm 0.618            0.226              1.226  1001.226 

6  Submerged  75  cm 0.561            0.250            75.250  1075.250 

Column  r  shows  that  a  bubble  emerges  with  an  infinitely  small 
change  of  radius.  In  fact  the  change  is  on  the  side  of  decrease  because 
of  the  surface  film  being  doubled.  Now,  since  there  is  practically  no 
expansion  or  contraction  upon  emerging  from  the  liquid,  it  seems  to 
me  that  "low  surrounding  atmospheric  pressure''  has  nothing  to  do 
with  bursting  Mr.  Callow's  bubbles.  Of  course  it  is  well  known  that 
if  a  gas  bag  is  burst  under  water  the  gas  remains  under  confinement ; 
whereas  if  it  is  burst  in  air  it  is  evanescent,  but  it  is  necessary  for  the 
metallurgist  to  study  the  texture  of  these  bags. 

Since  a  bubble  does  not  expand,  how  are  we  going  to  account  for 
"4-inch  bubbles"?  By  coalescence  (unless  electrification  plays  a 
part).  Sometimes  they  cohere  but  do  not  coalesce.  When  they 
coalesce  the  large  one  robs  the  small  one  because  pressure  varies  in- 
versely as  the  radius  (see  Equation  1).  The  little  one/ pumps'  its  gas 
into  the  large  one.  We  shall  have  to  learn  how  to  control  coalescence. 

Viscosity  is  another  important  factor  that  must  be  considered 
along  with  variable  surface  tension  and  coalescence.  It  is  not  surface 
tension  that  breaks  bubbles,  but  it  is  blows  upon  a  surface  that  lacks 
viscosity  or  toughness  and  variable  surface  tension,  that  cause  rupture. 
They  rupture  easily  on  account  of  lack  of  friction  of  the  molecules. 
With  low  friction  a  blow  is  likely  to  cause  the  molecules  to  be  sepa- 
rated a  distance  at  which  surface  tension  phenomena  disappear  before 
other  molecules  have  time  to  come  from  below  and  reinforce  the  area 
with  their  greater  surface  tension. 

The  books  all  emphasize  the  importance  of  great  superficial  vis- 
cosity and  small  internal  viscosity  for  the  persistence  of  a  froth.  It 
is  said  that  alcohol  which  has  a  superficial  viscosity  less  than  the 
internal  viscosity,  when  mixed  with  superficially  viscous  liquids,  will 
neutralize  the  relative  surface  viscosity  and  make  frothing  impossible. 
Hence  the  practice  of  adding  a  few  drops  of  alcohol  to  check  frothing 
in  pharmaceutical  work.  We  know  that  tannin  sometimes  interferes 
with  flotation  work  and  also  that  it  may  form  a  colloidal  solution  with 
water.  May  we  not  add  that  alcohol  and  tannin  are  deterrents  be- 
cause adsorption  is  checked  on  account  of  internal  viscosity  produced 
by  them  ?  For,  without  adsorption,  one  of  the  leading  factors  tending 


SMELTING  FLOTATION  CONCENTRATE  351 

to  produce  a  stable  froth  is  nullified,  that  is,  variable  surface  tension. 
My  best  thanks  are  due  to  Dr.  W.  B.  Anderson,  professor  of  physics 
in  the  College,  for  his  helpful  suggestions  and  critical  reading  of  these 
notes. 


SMELTING   FLOTATION   CONCENTRATE 

(From  the  Mining  and  Scientific  Press  of  February  12,^916) 

In  the  November  issue  of  Teniente  Topics,  the  monthly  publication 
of  the  Braden  Copper  Co.,  Chile,  a  member  of  the  staff  briefly 
outlines  the  development  of  the  smelter  from  1909  to  the  present 
time.  Metallurgical  difficulties  have  been  many,  but  were  overcome, 
in  spite  of  being  6000  miles  from  the  base  of  supplies.  The  plant 
now  treats  350  tons  of  concentrate  daily,  yielding  60  tons  of  copper, 
during  which  operation  60  tons  of  coke  and  10  tons  of  fuel-oil 
are  burned,  employing  350  men  and  1500  hp.  This  quantity  of 
concentrate  is  recovered  from  4000  tons  of  ore  crushed  per  day. 
The  concentrate  consists  of  19%  copper,  17%  silica,  23%  iron,  2% 
lime,  8%  alumina,  and  28%  sulphur.  It  is  sandy  and  slimy,  and 
contains  20%  water.  Of  the  350  tons  of  concentrate,  about  215  tons 
is  dumped  from  V-shaped  steel  cars  into  bins,  which  supply  the 
nodulizing  kilns.  This  concentrate  is  then  fed  to  conveyor-belts, 
thence  into  kilns,  heated  by  oil-burners  to  a  temperature  of  1750 °F. 
In  the  kilns,  the  sandy  concentrate  is  quickly  heated,  by  the  burning 
of  the  oil,  and  also  by  the  combustion  of  a  part  of  the  sulphur  content, 
to  a  sticky  consistence,  in  which  state  the  rolling  motion  tends  to  ball  it 
into  nodules  of  varying  size.  The  kilns  are  sloped  an  inch  per  foot 
toward  the  discharge-end,  out  of  which  the  red-hot  nodules  pour 
onto  an  endless  chain  of  cast-iron  pans,  which  convey  the  product 
to  hoppers  ready  to  charge  into  the  blast-furnaces.  The  nodules  have 
about  the  same  chemical  content  as  the  original  concentrate,  except 
that  the  proportion  of  sulphur  has  been  reduced  from  28  to  18%, 
and,  of  course,  the  moisture  has  been  evaporated. 

A  by-product  of  the  nodulizers  is  flue-dust,  that  is,  a  small 
proportion  of  the  concentrate  blown  out  by  the  draft  in  the  kilns 
and  caught  in  dust-chambers,  removed,  and  hauled  to  the  bins  for 
re-treatment. 

Another  50  tons  of  the  original  concentrate  is  sent  to  bins  that 
discharge  to  the  sinter-plant,  of  four  units.  Each  unit  is  a  concrete 
box.  4  ft.  wide  by  50  ft.  long.  In  place  of  a  top  there  is  a  cast-iron 
grate  similar  to  that  of  a  stationary  boiler,  but  with  smaller  air- 


352  THE  FLOTATION  PROCESS 

holes.  An  exhaust-fan  is  connected  to  the  box,  creating  a  strong 
down-draft  of  air  through  the  grate.  A  4-in.  layer  of  raw  concentrate 
is  spread  on  the  grate  with  an  inch  layer  of  saw-dust  ignited  with 
kerosene  or  gasoline  torches,  after  the  fan  has  been  started.  The 
saw-dust  starts  the  combustion  of  the  sulphur  in  the  concentrate. 
This  then  continues  to  roast  for  an  hour,  when  the  sulphur  is 
reduced  to  12%  and  the  loose  layers  are  reduced  to  a  hard  cake. 
The  cake  is  broken  into  pieces  six  to  eight  inches  in  diameter  and 
raked  into  cars  that  go  to  the  blast-furnaces. 

The  remaining  85  tons  of  concentrate  received  daily  is  discharged 
into  bins,  thence  fed  by  conveyors  into  cars  directly  to  the  blast- 
furnaces; this  amount  being  smelted  raw. 

The  two  blast-furnaces  are  25  and  30  ft.  long,  respectively,  4  ft., 
wide,  and  9  ft.  deep,  with  hollow-steel  water-jackets.  The  furnaces 
are  fed  with  a  charge  consisting  of  varying  proportions  of  nodulized, 
sintered,  and  raw  concentrates,  together  with  converter-slag  (con- 
taining 60%  iron)  as  a  flux,  and  coke  as  fuel.  The  proportion  of 
coke  to  concentrates  averages  about  15%,  and  is  dependent  directly 
on  the  amounts  of  raw  and  nodulized  concentrates.  This  mixture 
gradually  sinks  in  the  furnace,  becoming  hotter  and  continually 
melting,  until  in  the  bottom  it  is  liquid  at  a  temperature  of  2500 °F., 
and  runs  into  the  settler.  The  matte,  containing  45%  copper,  30% 
iron,  and  25%  sulphur,  remains  in  the  settler  until  removed  through 
a  hole  near  the  bottom  and  poured  into  the  converters  through  a 
brick-lined  launder. 

The  converters  are  of  the  Fierce-Smith  basic-lined  type.  Each 
consists  of  a  horizontal  cylindrical  sheet-steel  shell  25  ft.  long  by 
10  ft.  diameter,  inside  of  which  is  a  lining  18  in.  thick  of  magnesite 
brick.  This  material  is  not  attacked  by  the  chemical  reactions  in 
the  converter,  and  consequently  lasts  for  a  long  time,  unless  allowed 
to  over-heat.  The  cylindrical  converter-shell  rests  on  heavy  rollers, 
and  can  be  revolved  around  its  axis  so  as  to  empty  its  contents 
through  a  hole  in  the  side  when  necessary.  The  converter  is  pierced 
by  a  horizontal  row  of  blast-pipes  through  the  sheet-steel  and  lining, 
for  the  entrance  of  compressed  air.  These  holes  are  in  a  line  parallel 
with  the  axis  of  the  cylinder  somewhat  below  the  centre-line,  and 
point  down  toward  the  bottom  of  the  converter.  A  large  hole  in  the 
top  receives  the  charge  of  matte,  and  serves  as  a  chimney  for  the  escape 
of  gases. 

When  ready  to  receive  a  charge,  the  converter  is  revolved  until 
the  mouth  is  under  the  end  of  the  matte-launder  leading  from  the 


SMELTING  FLOTATION  CONCENTRATE  353 

settler  mentioned ;  this  position  places  the  tuyeres  at  about  the  centre- 
line of  the  cylinder.  A  stream  of  matte  is  run  by  gravity  into  the 
mouth,  until  the  converter  is  filled  almost  to  the  level  of  the  tuyeres. 
There  is  also  added  a  small  amount  of  quartz.  Compressed  air  at 
10  to  12  Ib.  pressure  is  then  forced  through  the  tuyeres  and  the 
converter  is  revolved  until  the  tuyeres  are  submerged  about  12  in. 
under  liquid  matte. 

The  elimination  of  the  iron  and  sulphur  leaves  practically  pure 
copper  as  the  only  remaining  constituent  of  the  matte ;  after  12  hours 
of  alternate  blowing-in  air  and  pouring  off  slag  a  bath  remains  of 
25  to  30  tons  of  molten  copper.  This  goes  into  ladle-cars  and  is 
hauled  to  a  receiver,  which  is  simply  a  huge  brick-lined  kettle  capable 
of  lifting  and  pouring  its  contents  into  a  series  of  moving  cast-iron 
molds. 

The  copper  solidifies,  is  removed,  and  carried  to  a  platform  to 
be  loaded  on  cars  for  shipment.  This  final  product  is  known  as 
'blister'  copper,  on  account  of  large  blisters  or  bubbles  of  gas  formed 
on  the  surface  of  the  bars  while  cooling.  The  bars  run  99.5%  copper, 
and  average  220  pounds  in  weight. 


354  THE  FLOTATION  PROCESS 

FLOTATION  ON  DUMP   ORE 

(From  the  Mining  and  Scientific  Press  of  December  11,  1915) 

The  Editor: 

Sir — On  the  eve  of  my  departure  from  Australia  I  received  a 
copy  of  your  issue  of  July  31,  in  which  considerable  prominence 
was  given  to  the  subject  of  flotation;  and  it  has  occurred  to  me 
that  the  following  may  be  of  interest  to  some  of  your  readers. 

Early  last  year  I  was  commissioned  to  re-organize  the  work  of 
the  Lloyd  Copper  Company  at  Burraga,  New  South  Wales,  and, 
upon  my  arrival  there,  found  that  the  concentration  mill  had  been 
equipped  recently  with  tube-mills  and  a  flotation  unit.  I  need  not 
go  further  into  the  description  of  the  plant  than  to  state  that  when  1 
assumed  command  the  output  of  the  mine  and  of  the  smelters  was 
limited  by  the  capacity  of  the  mill,  which  was  not  working  as  well 
as  it  should  have  been  doing.  Attention  was,  of  course,  first  given 
to  the  mill,  which  so  well  responded  to  the  efforts  made  that  before 
long  it  outstripped  the  supply  from  the  mine,  which  was  suffering 
sadly  the  consequences  of  lack  of  development.  In  the  meantime  I 
had  made  laboratory  tests  with  regard  to  the  flotation  of  the  tailing 
lying  on  the  dumps  and  had  also  sent  away  samples  for  trial  at 
the  experimental  works.  The  results  obtained  from  all  sources  showed 
that  the  sulphide  in  the  tailing  had  become  so  oxidized  that  it  had 
become  totally  unsuited  for  the  ordinary  process  of  flotation.  How- 
ever, before  finally  dropping  the  matter,  I  decided  to  give  the  tailing 
a  bulk  test  and  fed  it  to  the  mill  during  the  ordinary  course  of 
crude-ore  concentration.  By  this  procedure  I  obtained  such  satis- 
factory results  that  dump-tailing  was  put  through  the  plant  with 
the  crude  ore  whenever  a  shortage  of  the  latter  was  anticipated. 
In  order  to  find  out  definitely  what  recovery  was  being  made  from 
the  dump-tailing,  apart  from  the  mixture  of  tailing  and  crude  ore, 
an  eight-hour  run  on  tailing  by  itself  was  taken  in  hand.  For  the 
first  two  hours  of  the  run  everything  went  satisfactorily;  but  after- 
ward the  froth  began  to  thin,  and,  finally,  at  the  end  of  four  hours 
there  was  no  flotation  at  all,  the  particles  to  which  the  flotation  bubbles 
were  attached  rising  only  part  way  to  the  surface  in  a  manner 
similar  to  that  which  I  had  observed  in  my  initial  experiments  on 
the  flotation  of  zinc-blende  by  the  Potter  process  at  Broken  Hill 
in  1902.  The  addition  of  sulphuric  acid  and  other  chemicals  to 
the  eucalyptus  oil,  which  formed  the  frothing  medium,  had  no 
beneficial  effect. 


FLOTATION  ON  DUMP  ORE  355 

At  the  end  of  four  hours  crude  ore  was  put  into  circulation  in 
the  mill  again;  and  very  shortly  afterward  frothing  recommenced, 
with  the  result  that  the  flotation  of  the  mixture  of  crude  ore  and 
tailing  proceeded  satisfactorily.  Similar  results  were  obtained  during 
all  the  subsequent  trials. 

As  my  records  are  stowed  away  in  the  hold  of  this  steamer,  I  am 
not,  at  the  present  moment,  able  to  give  accurate  figures  as  to  the 
recoveries  obtained. 

In  smelting  the  flotation  concentrate  great  losses  were  at  first 
encountered.  A  big  proportion  by  weight  was  lost  in  the  roasters 
and  again  when  the  calcined  concentrate  was  charged  into  the 
reverberatory  furnaces.  Clouds  of  calcined  flotation-concentrate 
could  be  seen  issuing  from  the  top  of  the  chimney-stack  whenever 
the  feed-hoppers  containing  the  calcine  were  opened  and  the  charge 
dropped  into  the  furnaces.  All  kinds  of  devices  were  tried  to  over- 
come these  losses,  but  they  proved  unsuccessful.  As  a  final  resort 
the  'green'  concentrate,  after  having  been  well  drained,  was  fed 
through  the  side  doors  (the  rabbling  doors)  of  the  reverberatories 
and  this  procedure  was  ultimately  adopted  with  satisfactory  results. 
As  the  reverberatories  frequently  got  ahead  of  the  output  of  the 
mine  and  mill,  they  were,  from  time  to  time,  used  as  roasters  by  being 
fully  charged  with  'green'  flotation-concentrate  and  run  with  open 
doors  for  several  hours  until  calcination  had  been  completed. 

I  may  add  that  at  the  works  of  the  Wallaroo  &  Moonta  company 
it  has  been  found  convenient  to  add  to  the  top  of  each  charge  in 
the  blast-furnace  a  definite  quantity  of  'green'  flotation-concentrate, 
which  sinters  as  the  charge  sinks  and  reaches  the  solidified  stage 
before  entering  the  strong  blast  area. 

V.  F.  STANLEY  Low. 

R.  M.  S.  Ionic,  October  1. 


356  THE  FLOTATION  PROCESS 

SIMPLE   PROBLEMS   IN   FLOTATION 

(From  the  Mining  and  Scientific  Press  of  February  19,  1916) 
The  Reader: 

Sir — On  another  page  Mr.  Durell  objects  to  a  statement  of  mine  in 
regard  to  the  floating  of  an  ungreased  needle  on  water.  He  is  meas- 
urably right.  An  ungreased  needle  will  float,  but  not  nearly  so  easily 
as  the  greased  one.  The  latter  will  float  if  placed  on  the  water  with- 
out special  care,  but  if  the  former  is  handled  in  the  same  way  it  will 
sink.  My  reference  to  the  matter  was  quoted  from  the  'prior  art/ 
which  in  this  regard,  as  in  many  others,  I  know  now  to  be  a  dangerous 
guide.  Some  time  ago,  but  since  my  first  writing  on  flotation,  last 
summer,  I  made  several  experiments  to  find  out  for  myself  what 
happens.  To  be  certain  that  the  needle  was  free  from  grease,  I  dipped 
it  in  a  hot  solution  of  washing-soda  and  then  dried  it,  taking  care  to 
use  a  clean  cloth  and  to  not  touch  it  with  my  fingers.  Then  I  placed 
a  piece  of  tissue-paper  on  the  water  in  a  cup  and  laid  the  needle  upon 
it  by  aid  of  a  pair  of  pincers.  The  tissue-paper  was  depressed  into 
the  water,  becoming  wetted  gradually,  until  it  was  all  soggy  and 
finally  sank,  leaving  the  needle  floating.  Without  such  care  I  could 
not  make  the  needle  float. 

Next  I  used  the  camphor  test  to  ascertain  if  the  water  had  been 
contaminated  by  grease.  If  camphor  is  whittled  with  a  knife  above 
the  water,  the  shavings  will  dance  on  the  water  in  a  life-like  manner 
suggesting  insects  in  a  fit.  This  phenomenon,  as  shown  by  Marangoni, 
is  due  to  the  dissolving  of  the  camphor,  preferably  at  its  pointed  end, 
where  a  maximum  surface  is  presented  to  the  water.  The  solution 
decreases  the  surface  tension  of  the  water  in  contact  and  thereby 
causes  the  uncontaminated  water,  with  its  stronger  tension,  to  pull 
away  from  the  spot  affected  by  the  camphor.  In  order  to  produce 
this  activity  of  the  camphor,  the  surface  tension  of  the  liquid  must 
be  greater  than  that  of  the  camphor  solution.  Hence  if  grease  be 
introduced  into  the  water,  thereby  lowering  its  surface  tension,  the 
camphor  becomes  inert.  If,  while  the  camphor  particles  are  active, 
the  water  is  touched  by  a  greasy  finger  (all  fingers  are  a  little  greasy) 
the  camphor  becomes  quiet  immediately.  This  furnishes  a  good  test 
for  the  presence  of  even  a  trace  of  grease.  No  ordinarily  *  clean '  cook- 
ing utensil  is  sufficiently  free  from  grease  to  allow  an  exhibition  of 
the  camphor  dance. 

To  return  to  the  floating  ungreased  needle.     I  introduced  some 


SIMPLE  PROBLEMS  IN  FLOTATION  357 

camphor  shavings,  and  they  were  lively.  Then  I  repeated  the  experi- 
ment with  a  needle  that  was  slightly  greased,  and  the  camphor 
seemed  to  be  unaffected  thereby.  Finally,  I  smeared  the  needle  with 
olive  oil :  an  iridescence  on  the  surface  of  the  water  indicated  diffusion 
of  the  oil.  This  time  the  camphor  chips  fell  dead  on  the  water,  and 
remained  wholly  inert.  Apparently,  therefore,  the  needle  will  hold  to 
itself  a  limited  amount  of  oil  or  grease,  which  adheres  so  selectively 
as  not  to  contaminate  the  water.  But  any  excess  of  oil,  more  than 
the  needle  can  hold,  will  be  set  free  to  modify  the  water  and  lower  its 
surface  tension. 

Of  course,  there  is  a  limit  to  the  size  of  needle  that  can  be  floated. 
When  the  needle  is  floating  it  lies  in  a  dimple  or  depression;  if  the 
needle  is  so  heavy  as  to  overcome  the  surface  cohesion,  the  sides  of 
the  depression  meet,  and  the  needle  is  engulfed  in  the  water.  Bubbles 
of  air  can  be  seen  attached  to  the  needle  when  floating.  The  film  of 
air  is  not  continuous.  Apparently  the  flotation  is  due  to  the  resist- 
ance of  the  water  surface  to  rupture,  this  resistance  being  caused  by 
an  elastic  force  that  permits  the  water  to  yield  in  the  form  of  a  dimple. 
Moreover,  the  air  bubbles  add  to  the  buoyancy,  both  by  their  less 
specific  gravity  and  by  preventing  the  curved  walls  of  the  dimple 
from  meeting  overhead,  that  is,  by  widening  the  angle  of  contact.  As 
the  proverb  says,  ' '  oil  and  water  will  not  mix ; ' '  the  adhesion  of  air  to 
a  metallic  surface  is  matched  by  the  molecular  repulsion  between  the 
oil  and  the  water. 

As  Mr.  Durell  suggests,  the  fact  that  grease  is  not  essential  to  the 
floating  of  the  needle  is  symptomatic  of  the  trend  of  the  flotation 
process.  The  oil  is  important  chiefly  as  a  means  of  lessening  the 
surface  tension  of  the  water  and  so  yielding  air  bubbles  that  will  last 
long  enough  for  the  work  of  buoying  the  mineral  particles. 

Permit  me  to  continue  to  disagree  with  Mr.  Durell  as  to  the 
negligibility  of  viscosity  in  the  formation  of  froth.  In  quoting 
Danniell,  I  was  not  so  out  of  date,  for  the  reference  was  to  the  edition 
of  1911.  "We  shall  hear  more  about  viscosity  in  the  near  future. 

In  regard  to  the  attachment  of  previously  formed  bubbles  to 
metallic  particles :  this  point  has  been  elucidated  by  the  cinema  record 
of  experiments  presented  in  the  Miami  case.  Apparently  such  bub- 
bles do  attach  themselves  to  the  metallic  particles,  even  when  un- 
oiled. 

In  regard  to  the  experiment  described  and  discussed  by  Messrs. 
Durell  and  Norris,  I  have  tried  it  and  I  recommend  every  student 
of  flotation  to  try  it,  watch  it,  and  cogitate  on  it.  If  kerosene  oil  is 


358  THE  FLOTATION  PROCESS 

poured  over  colored  water  and  air  is  blown  into  the  lower  liquid,  a 
number  of  interesting  phenomena  can  be  observed.  Mr.  Durell  sees 
bubbles  enclosed  in  a  film  of  the  colored  water  rising  through  the 
oil  and  breaking  at  the  surface,  while  the  colored  water  of  the  bubble- 
film  drops  back  through  the  oil  exactly  as  a  balloon  on  bursting  drops 
to  the  earth.  Mr.  Norris  conducts  the  experiment  in  two  stages;  in 
the  first,  he  blows  air  gently  and  sees  colorless  bubbles  rising  from  the 
colored  water  through  the  oil  to  the  surface;  he  says  that  these 
bubbles  show  no  trace  of  color,  and  they  are  unaccompanied  by  a 
return  passenger  of  colored  water.  He  concludes  that  the  bubbles 
have  no  film,  but  are  simply  holes  in  the  water  and  oil  successively. 
In  the  second  stage  of  his  experiment,  he  injects  air  with  greater 
pressure,  making  larger  bubbles,  which  pull  the  colored  water  to  the 
surface  of  the  oil.  The  bubbles  are  not  colored,  but  they  take  with 
them  flat  portions  of  the  colored  water,  which  fall  back  when  the 
bubbles  reach  the  surface  of  the  oil. 

I  have  conducted  the  experiment  many  times,  and  my  report  is  as 
follows:  When  the  air  is  injected  into  the  oil,  the  bubbles  are  short- 
lived, but  they  last  long  enough  to  prove,  as  we  know  already,  that 
the  oil  is  not  a  pure  and  perfectly  homogeneous  liquid.  In  such  a 
liquid,  bubbles  would  not  survive.  The  fact  that  two  bubbles  can 
touch  without  coalescing  proves  that  there  is  a  film  or  membrane  sep- 
arating and  surrounding  them.  When  I  blow  air  gently  into  the 
colored  water,  the  rising  bubbles  are  colorless.  They  accumulate  at 
the  surface  of  the  oil,  and  show  an  attraction  for  each  other,  and  for 
the  sides  of  the  glass  vessel.  These  bubbles  appear  to  last  longer  than 
those  blown  in  the  oil.  Next,  when  I  inject  air  more  rapidly  into  the 
water,  a  bubble  appears  at  the  point  of  a  cone  or  mound,  as  if  it  were 
dragging  the  water-surface  with  it.  This  bubble  will  remain  poised 
for  awhile  at  the  peak  of  the  mound  of  water  before  breaking  away 
and  rising,  while  the  water  falls  back.  If  the  air  be  injected  still  more 
rapidly,  the  bubble  breaks  through  the  water-surface,  appearing  to 
tear  it,  and  takes  with  it  a  portion  of  water.  This  is  attached  to  the 
south  pole  of  the  bubble  and  may  accompany  it  to  the  surface,  where, 
on  arrival,  it  drops  away  in  a  curious  crescent  form.  If  I  introduce 
air  still  more  rapidly,  the  water-surface  is  torn  into  pieces  of  odd 
shape  by  the  rising  bubbles. 

The  bubbles  in  oil  are  round  or  spherical;  those  generated  in  the 
water,  as  seen  in  their  passage  upward  through  the  oil,  are  flattened ; 
they  are  oblately  spheroidal.  The  colored-water  drop  that  leaves  the 
south  pole  of  the  bubble,  on  its  arrival  at  the  surface,  is  also  flattened ; 


SIMPLE  PROBLEMS  IN  FLOTATION  359 

if  small,  it  is  crescent-shaped;  if  larger,  it  is  oblately  spheroidal  or 
lenticular. 

It  will  be  noted  that  I  have  said  that  this  and  that  "appears"  to 
take  place.  The  difference  in  description  by  various  observers  indi- 
cates how  difficult  it  is  to  see  correctly.  These  are  truly  '  phenomena, ' 
or  appearances  that  are  unusual  and  hard  to  explain. 

As  to  Mr.  Norris's  idea  that  the  bubble  is  simply  a  hole  in  the 
liquid,  I  would  suggest  that  a  globule  of  air  takes  to  itself  a  film  when 
in  an  impure  liquid,  that  film  containing  some  impurity  or  con- 
taminant in  concentratable  form.  Thus  the  hole  becomes  a  sac.  As 
the  colored  water  and  the  kerosene  are  both  impure  liquids,  we  may 
infer  the  existence  of  a  film  on  the  globule  of  air,  as  indeed  is  proved 
on  its  arrival  at  the  surface,  where  bubbles  remain  in  contact  without 
coalescing.  The  next  question  arising  is  as  to  what  change  the  film 
of  the  bubble  undergoes  in  the  passage  of  the  bubble  from  one  liquid 
into  the  other.  The  watery  film  would,  I  suppose,  be  affected  by 
coming  in  contact  with  the  oil,  and  it  would  seem  to  me  a  priori  that 
the  bubble  would  arrive  with  a  film  of  the  liquid  having  the  lower 
surface  tension.  This  is  a  point  I  would  like  to  refer  to  our  friends, 
Messrs.  Ralston,  Durell,  Norris,  and  Coghill,  all  of  whom  have  con- 
tributed so  generously  and  so  usefully  on  .the  theory  of  the  subject. 
That  theory  is  no  mere  academic  exercise;  it  is  at  the  very  base  of 
any  reasoned  understanding  of  the  flotation  process. 

T.  A.  RICKARD. 
San  Francisco,  February  11. 


INDEX 


Page 

Absorption    346 

Adsorption    347 

Acid,    effect   of 131,157 

Flotation  method    147 

For  preferential  effect 259 

Sludge    69 

Used  at  Anaconda   106 

Acidity  of  pulp 229 

Adhesiveness  of  oil  and  water.   182 

Agitation,  froth  method 149 

In   Pachuca   mixer 235 

Air,  adhesiveness  of 14,     15 

Adhesion  of  bubbles  to  par- 
ticles        187 

And  bubbles  343 

Bubbles    198 

Contact,   metallic   particles..   201 

Froth  flotation  159 

In  flotation   268 

Introduction  of    153 

Used  in  Elmore  process 25 

Alkalinity 93 

Effect  of    318 

Allen,   Glenn  L.     Testing  ores 

for  flotation  277,  293 

Anaconda  Copper  M.  Co 51,  106 

Anderson,   W.    B 351 

Arizona  Copper  mill   236 

Australian  practice   320,  354 

Treatment  of  flotation  residue  255 

Bacon,  R.  C 185 

Bains,  Thos.  M.,  Jr.,  Electrical 

theory   of   flotation 225,  258 

Ballantyne,  W.  H 273 

Blende,  preferential  flotation . .  259 

Block,  James  A 244,  324 

Why  is  flotation?   187 

Boyle's  law   349 

Braden  copper  mill   351 

Bradford  method    18 

Bradford,    L.,   process 81 

Bubble  and  air  particles 343 

Bubbles,  armoring  of 133 

Electrification  of   226,  338 

Bursting     13 

Formation  of   358 

Of   carbon   dioxide 279 

Surface    tension    of . .  .   313 


Page 

Bulk-oil  flotation 145 

Oil  methods   130 

Butters,  Charles.    Cyanide  treat- 
ment of  concentrate 203 

Flotation  of  gold  ores 276 

Treatment  of  concentrate .  59,     89 

Caldecott  cones   254 

Callow,  J.  M.     Notes  on  flota- 
tion       231 

Callow  cell  106,  204 

Capacity  of  239 

Flotation  of  copper  ores 65 

Machine 242,  243 

Method    67 

Patents    48 

Plant  at  Inspiration    88 

Testing  machine    294,  298 

Campbell,  D.  G 227 

Camphor  test   356 

Canby,  R.  C 33 

Capacity  of  Callow  cell 239 

Capillarity   10 

Carbonates,  effect  of 265 

Case  machine  305 

Case  School  of  Applied  Science  258 

Cattermole,  A.  E 40,   71,  193 

Method 29,  113,  149 

Patent    41 

Chalmers  &  Williams  mill 84 

Chapman,  G.  A 114 

Chlorination    applied    to    flota- 
tion concentrate    220 

Clennell,  J.  E.     Cyanide  treat- 
ment  of  concentrate 203 

Coagulation    149,  246 

Coal-tar  products    239 

Coghill,  Will  H.     On  froth....   344 

Surface  tension   154 

Colloidal  impurities,  effect  of. .   245 

Concentrate,  cleaning  of 286 

Concentrate,  silicious 55 

Smelting   of    351 

Treatment  of 59,     89 

Conductivity,   electrical    338 

Contact   angle    182 

Copper  ores   48 

Sulphate    266 

Cost  of  flotation 99,  243 

Of  test  machine   .  .  298 


362 


INDEX 


Page 

Coutts,    J 302 

Courtney,  C.  F 113 

Cresylic  acid   62,     94 

Crushing   before    notation 

58,  84,  120 

Fine   sulphide    291 

Cyaniding  and  flotation,  treat- 
ment after  roasting 207 

Cyaniding    raw    flotation    con- 
centrate       221 

Daly- Judge   mill    238 

De  Bavay  method 24,  323 

Deister  concentrators   89 

Delprat,  G.  D 37,  147 

Process   320 

Density  of  pulp 238 

Of  surface  film 183 

Dielectrics    228 

Differential    method    142 

Disposal  of  residue   248 

Dorr  thickeners   106,  254 

Draining   flotation    concentrate 

248,  252 
Drucker,    A.    E.     Flotation    of 

gold    ores    224 

Dump  ore,  flotation  of 354 

Durell,     C.     Terry.     Flotation 
principles 319 

Why  do  minerals  float? 175 

Electric    charges    185 

Electrical   conductivity   of   sul- 
phides      227 

Theory   185,  245,  258,  335 

Elmore,  Francis  E 36 

Machine    294 

Method  25,  34,  150 

Process  in  Australia 54 

Elmore  vacuum  process   

34,  44,  145,  321 

Emulsification    13 

Everson,   Carrie    J 35,  145,  190 

Fahrenwald,     F.     A.     Electro- 
statics       335 

Film,  insulating   228 

Filtering   concentrate    248 

Flotation,  a  paradox 267 

Air-froth    159,  189 


Page 
Flotation: 

At  Anaconda    106 

At   Broken    Hill 29,  319 

At  the  Central  mine. 110 

At  Mt.  Morgan    53 

By  acid  37,  279 

By   agitation-froth    281 

Cells  in  series   237 

Classified    33 

Concentrate,  cyaniding   203 

Concentrate,   raw  cyaniding.  221 

Concentrate,  chlorination  of.  220 

Effect  of  soluble  component.  263 

Electrical  theory    225,  258 

Electro-statics    of 335 

History  of  231 

In  Australia. 29,  47,  110,  151,  319 

In  a  Mexican  mill 91 

In  Mexico   267 

Of  copper  ores 65 

Of  gold  ores.   A.  E.  Drucker.  224 

Of  gold  ores  276 

On  dump  ore   354 

Pneumatic    233 

Preferential    71,  258 

Prime   requisites   136 

Principles    319 

Process,  the    9 

Recovery  at  Mt.  Morgan ....  53 

Selective    *332 

Simple  problems  S56 

Smelting  of  concentrate 351 

Testing  ores  277 

Tests    92 

Theories     244 

Use  of  lime  265 

v.  cyanidation 99 

Flow-sheet  of  Inspiration  mill.  89 

Fouling  of  solution 263 

Froment,  Alcide    39 

Patent    272 

Process    148 

Froth  and  flotation 102 

Agitation,  discovery  of 118 

Character  of  241 

Destruction  of   331 

Disposal  of  303 

Early  attempts  in  Australia.  110 

Formation   .                               .  237 


INDEX 


363 


Page 

Froth  and  flotation: 

Relative  persistence    31,  170 

Science  of   344 

Frothing    281 

Gabbett  mixer  200 

Gas,  use  of  139 

Effect   of 325 

Glass  jar  machine    295 

Greenway  &  Laury  method. ...  79 

Grinding  for  tests 300 

Handling  of  slime   257 

Hardinge    mill    84,  106 

Haynes,  William   34 

Hebbard,  James  29 

Flotation  at  the  Central  mine  110 

Machine    87 

Higgins,  Arthur  H 149,  153 

Hoffman's  results   180 

Hoover  machine. .  .49,  287,  288,  289 

Hoover,  T.  J 47,  158,  322,  331 

Horwood   process    75 

Hyde,  James  M 31,  48,  290 

Hyde's   patent    150 

Hydrates,  effect  of 265 

Hydrogen-sulphide  gas   188 

Ingalls,   W.  R 14,  19 

Inspiration  Consolidated  C.  Co.  51 

Mill    234 

Mill,  power  consumed 241 

Mine,  flotation  at 83 

Oil  used  at  69 

Janney,  F.  G 283 

Flotation    machine.  .146,  281,  283 
Test-machine    285 

Kenyon,  W.  H 197 

Kirby,  E.  B.,  patent 44,  147 

Krupp  ball-mill   121 

Laboratory  work 299 

Lead  ore,  preferential  flotation  259 

Liebmann,  Adolph    33 

Lime  hydrate  method 265 

In  flotation   265 

Use  of 101 

Litigation    159 

Lloyd's  Copper  Company 354 

Low,  V.  F.   Stanley .   355 


Page 

Lyster  process  77 

Machine    287 

Macquisten  method    144 

Tube    19,  278 

Magistral  mill   267 

Marcy  ball-mill    85 

Mathewson,   E.   P 106 

Mexican  mill,  flotation  in 91 

Miami  experimental  plant 161 

Method   33 

Process   at    167,  169 

Mickle,    Kenneth   A 15,  141,  324 

Minerals    Separation. .  .54,  269,  275 

And  Froment  40 

Basic  patent    30,     42 

Machine    86 

Organization    29 

Patent    ...150,  152,  163,  167,  272 

Plant  122 

Royalties    50 

Mitchell,   D.  P 43 

Molecular  forces  308 

Morning  mill   233 

Motherwell,  Wm.     Flotation  at 

the  Inspiration  mine 83 

Flotation  at  Mt.  Morgan   ...     53 

Moulden,   J.   C 114 

Mount  Morgan,  flotation  at 53 

Nascent,  definition  of 325 

National   copper  mill 68,  232 

Needle,    floating   of 326,357 

Norris,    Dudley  H 187,  323 

Flotation,  a  paradox 265 

Molecular  forces   308 

Patent    45,  269,  274 

Nutter,   E.   H 48 

And  Lavers  patent  78 

Occlusion,  definition  of 328 

Of  gas  140,  176 

Oil,  consumption  of 70,  240 

Bulk  methods  130,  145 

Function  of  330 

Pine  63,  241 

Proportion  of  16,  43 

Substitutes  153 

Oiling  of  mineral  particles 322 

Oils 94,  123 


364 


INDEX 


Page 
Oils: 

Creosote 241 

Solubility    of    348 

Testing  of  301 

Used    in   flotation 60,  153,  239 

"    at  Mt.  Morgan 56 

"     in    Wood    machine 280 

Oliver   filters    108 

Osmosis,    description   of 332 

Owen,   T.   M 294 

Testing    machine    296 

Patents    34 

Physics  of  flotation    9 

Picard,  H.  F.  K 33 

Pine   oil    63,  241 

Oil  as  frother   239 

Pneumatic   flotation    233,  294 

Potter   apparatus    38 

Charles  V 37,  147 

Method    23 

Power  for  flotation  machines. .   241 

Preferential   flotation    71 

Psychology   of   flotation 47 

Ralston,     O.     C.     Preferential 

flotation    71 

Testing   ores   for .  flotation . . 

277,  293 

Why  do  minerals  float? 175 

Ramage,   A.   S 73 

Heinders'  researches   178 

Revett,  Ben  S 9 

Rickard,    T.    A 344,359 

The  flotation   process   9 

What    is    flotation? 126,  144 

Roasting  flotation  concentrate.  213 

Robson,  George   36 

Rolker,  Chas.  M 151 

Royalties    50 

Avoidance  of   275 

Salt,    effect   of 103 

Salts  in  solution 154 

San  Francisco  del  Oro  mill 145 

San  Sebastian  ore   208 

Saponine,  effect  on   froth 14 

Scott,  Walter  A.    On  air-froth.  159 

Separatory  funnels  for  testing.  293 
Shellshear,     W.     Disposal     of 

residue    ,                              .  248 


Page 

Silica  in  concentrate  55 

Silver  ores,  treatment  of 91 

Slide  machine    291 

Smelting   concentrate    351 

Smith,  Ralph   290 

Soap-bubbles    10,  132,  160 

Soluble   component,   effect   of. .   263 

Salts    94 

Spitzkasten,  shape  of    282 

Stability  of  film    345 

Sulitelma    plant    28 

Sulman,   H.    L 149 

Sulman  &  Picard  patent 

44,  144,  153,  164 

Sulphates,  effect  of   264 

Sulphonation    61 

Surface  compression    308 

Tension.  10,  126,  138,  162,  183,  344 

"     effect  of   177 

"     in     bubbles    313 

"     measurement.il,    127,  158 

"     and  salts  in  solution.   154 

Swinburne,   J 326 

Tension,  interfacial 178 

Testing  machines   285,  287, 

288,  291,  293,  295,  296,  298 

Tests,  separating  funnel    318 

Thickeners  for  concentrate 250 

Thickeners    for    draining    con- 
centrate       253 

Tonnage  treated  by  flotation . .       9 

Towne,  R.  S 48 

Towne-Flinn  plant   87 

Tunbridge  patent   191 

Vacuum  method    27 

Viscosity    129,  329,  350 

Wallaroo  &  Moonta 355 

Washoe  Reduction  Works. ....  106 

Water,  electrification 340 

Wentworth,  H.  A 73 

Williams,   Henry  D 189 

Wood,  H.  E 20,  21 

Wood  machine  280 

Method    145 

Oils  used  69 

Zinc  separation  from  galena. . 

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